Lava Thickness Research Articles

On the variations of flow rate in non-explosive lava eruptions

A physical model is developed to determine factors which influence the dynamics of non-explosive lava eruptions. In the model, magma rises in a laminar regime from an overpressured chamber surrounded by elastic rock and erupts at the surface, where the accumulation of lava may alter the vent pressure. In a flow rate versus volume diagram, an eruption follows a path which is sensitive to relative changes in flow variables such as viscosity, conduit dimensions and thickness of lava over the vent. The path does not depend on the unknown elastic properties of the country rock or the chamber dimensions. With appropriate volcanological data, an observed flow rate versus volume path can be interpreted. The approach is applied to three well-documented eruptions. In each case the eruption rate was partially influenced by decreasing chamber pressure. The 1988–1990 eruption of Lonquimay (Chile) exhibits an early phase of conduit shrinkage which lasted about 100 days, probably due to magma solidification against country rock. The 1979 eruption of La Soufrière de Saint Vincent (West Indies) was initially affected by lava dome growth and later passed through a phase possibly caused by constriction of the conduit. The 1943–1952 eruption of Paricutín (Mexico) was affected by changes of lava level in the cinder cone and magma properties. In these three eruptions, the pre-eruptive chamber overpressures were similar (10–20 MPa) even though the erupted volumes differed by as much as two orders of magnitude.

Geophysical models of the Kenya rift

Geophysical models of the Kenya rift before 1990, based on gravity and seismic data, showed that the crustal structure beneath the rift is different’ from that beneath the flanks. The early pendulum gravity measurements of Bullard (1936) revealed that the East African plateau is in isostatic equilibrium and that the adjoining Western and Eastern rifts are associated with broad negative anomalies. Subsequent work focussed on the presence within the broad negative of a narrow axial positive anomaly first identified, but not analysed by McCall (19671, in the vicinity of Menengai. This feature was mapped in some detail along the rift’s length by Searle (1970) between the equator and 1.25”s where it was found to be continuous but variable in amplitude. He explained the positive anomaly in terms of a dense intrusion about 20 km wide, with its top within about 3 km of the surface. Fairhead (1976) reinterpreted one of Searle’s profiles through Nairobi and Suswa using a different regional, which reduced the amplitude of the positive anomaly by half. His favoured model included a dense dyke injection zone 10 km wide intruding a 2 km thickness of basaltic lavas filling the rift floor below 2 km of less dense phonolite lavas. Baker and Wohlenberg (1971) reinterpreted one of Searle’s profiles just south of Menengai to obtain a much-quoted model for the crust and

Heat loss and tectonic style of Venus

The tectonic style of a terrestrial planet depends strongly on the mechanisms of heat release from the mantle through the lithosphere to the surface. Three types of lithospheric heat transfer have been proposed. (1) Lithospheric conduction, (2) (hot spot) volcanism, (3) plate recycling (mainly at spreading plate margins). In the case of the Earth the total heat flow is determined by plate recycling 65%, heat conduction through the lithosphere 20%, decay of radioactive elements in the crust 15%, hot spot volcanism <1%. Scaling the mean surface heat flow density of the Earth to venusian conditions leads to 66 mW/m2. In the case of Venus plate tectonics play only a minor role. Thus, two processes remain for heat release: (hot spot) volcanism and conduction. The term “hot spot” is written in brackets because volcanism on Venus occurs globally, not necessarily associated with hot spots. The volcanic lava production has been estimated from Venera 15/16 scenes. Arecibo and Magellan images revealed that the surface character south of 30° N is very similar to the area covered by Venera. The main results of the estimation are: (i) The maximum thickness of the plain lavas is 3 km. (ii) With plain lava thicknesses larger than 200 m the lava production from central volcanoes is negligible, (iii) Two age models have been used for the mean age of the area obseved: Δt 1 = 109 a, Δt 2 = 400 x 106 a. Δt 1 leads to the maximum lava production rate of 3 km3/a compared to 20 to 25 km3/a of the Earth; this gives a maximum contribution of 0.75mW/m2 to the heat flow density of Venus, i.e. about 1%. This implies that either heat conduction is the only dominating process for heat release or there is a hidden reservoir of the “missing basalt” somewhere or there is another unknown tectonic process. Assuming pure conduction and correcting the surface heat flow density for radioactive elements in the crust leads to a thickness of the thermal lithosphere of 45km. A reservoir for the “missing basalt” could be basaltic underplating to a depth of 100 km. This gives a contribution of about 20 mW/m2 with the age model δt 2 to the heat flow density from first order calculations. While the tectonic style of the Earth can be described to be linear formed at the plate margins, the surface of Venus is characterized by global spotty volcanism. The surface is more dominated by volcanic landforms than in the case of the Earth despite the relatively low lava production rate with a maximum of 3 km3/a. As plate tectonics is a minor process on Venus, conduction through a rather thin lithosphere should play an important role for heat release.

Magnetostratigraphy and geochronology of northwest Iceland

The NW peninsula of Iceland is built mainly by tholeiitic, low K flood basalts that show a regional southeasterly dip, generally of less than 10°. From the lavas mapped and drilled for paleomagnetic measurements (a total of 1261 flows), two continuous composite sections were constructed, one on the western side of the peninsula 4055 m thick comprising 456 lavas and the other adjacent to the east coast, 3165 m thick comprising 396 lavas. K‐Ar age measurements were made on more than 70 lavas distributed throughout the two sections. These two lava sequences are about 90 km apart along strike, and although direct stratigraphic correlation is not possible between them, the evidence indicates that the eastern section is stratigraphically younger than that in the west, with some overlap. The results show that the lava sequences were erupted over an interval extending from about 14 to 8 Ma ago in the middle to late Miocene. Remarkably linear relations are found between the measured age and cumulative stratigraphic thickness for both sections, indicating rather uniform local rates of growth of the lava piles. For the western composite section a growth rate of 1820 m/Ma is found, contrasting with a much lower growth rate of 670 m/Ma for the eastern sequence. The average thickness of individual lavas in both sections is close to 8 m. The average time between eruptions of lavas in the western section is 5000 years, compared with a value of 12,000 years for the eastern section. The regional geology together with our measurements are interpreted in terms of crustal accretion processes by which the NW peninsula of Iceland was constructed by eruption of lavas from a spreading center of northeasterly strike. It is not clear whether the differences in rates of growth of the lava pile in the western and eastern sections are because of variation in eruptive activity with time or because eruptive activity has varied along the strike of the spreading center. Paleomagnetic measurements on the lavas provide a detailed history of polarity of the geomagnetic field during the interval 14–8 Ma ago. For the eastern composite section there is excellent and unambiguous correlation of the observed polarity pattern with the marine magnetic anomaly record. From these data we obtain an age of 9.6 Ma for the younger boundary of marine magnetic anomaly 5Table 1 is available with, entire article on microfiche. Order from American Geophysical Union, 2000 Florida Ave., N.W., Washington, D.C. 20009.

Lava flooding of ancient planetary crusts: Geometry, thickness, and volumes of flooded lunar impact basins

Estimates of lava volumes on planetary surfaces provide important data on the lava flooding history and thermal evolution of a planet. Lack of information concerning the configuration of the topography prior to volcanic flooding requires the use of a variety of techniques to estimate lava thicknesses and volumes. A technique is described and developed which provides volume estimates by artificially flooding unflooded lunar topography characteristic of certain geological environments, and tracking the area covered, lava thicknesses, and lava volumes. Comparisons of map patterns of incompletely buried topography in these artificially flooded areas are then made to lava-flooded topography on the Moon in order to estimate the actual lava volumes.

Reply to 'Tectonic contrasts in the Southern Uplands'

SIRS — Attention has recently been drawn (Weir 1979) to the variation in exposure width of the Moffat Shale belts of the Southern Uplands. This, it has been suggested (op. cit. pp. 175-7), is caused by the exposure of different structural levels of a curved zone as a result of very large-scale open folding on an approximately N-S axial trend: the broad outcrops of shale corresponding to culminations above igneous plutons with the narrower outcrops formed by the exposure of a higher structural level in depressions between plutons. This intriguing idea raises a number of questions, not least the coincidence of depressions with the Cairnsmofe of Carsphairn and the Culvennan Fell intrusions. However, of more general significance may be the original variation in the stratigraphic thickness of the Moffat Shale sequences. In most of the inliers true black shale forms only a small proportion of the total thickness, the remainder being composed of siltstone, fine greywacke, chert and lava. The first two of these lithologies probably represent distal turbidite deposits and their thickness may well vary along strike relative to the origins of the depositing turbidity currents. Lava thicknesses will, of course, be very variable laterally and cherts too may be thickly developed in places and absent elsewhere. Thus, for example, of the wide Moffat Shale outcrops shown N of Glenluce (Weir 1979, fig. 2, culmination 1) the northernmost is composed in the main of fine greywacke and does not form a recognizable outcrop on Sheet 3 (Stranraer) of the one-inch Geological Map, and the southernmost contains a large proportion of chert, together with some lavas and intrusive dolerites. It is doubtful whether any valid conclusions can be drawn from a comparison of the exposure width of the latter outcrop with the narrower part of the same shale belt to the NE where, in a sequence several hundred metres thick, up to 20 thin shale horizons are interbedded with siltstones and fine grey wackes with only very rare chert (Stone 1980).

Geomorphological observations at Kangerdlugssuaq, East Greenland

The Kangerdlugssuaq area is mainly comprised of two contrasting rock groups: on the one hand the easily-eroded lavas and sediments of late Mesozoic to early Tertiary age and on the other the highly resistant Precambrian gneisses. Intermediate between these two types in terms of behaviour with respect to erosion are the Tertiary plutonic complexes and the basaltic areas along the coast which have been intruded by intense dyke swarms.&#x0D; In the late Mesozoic the area was a peneplain, and low relief apparently persisted throughout the volcanic episode as there is good evidence that the lava plateau subsided during its formation. During this period ocean-floor spreading gave rise to the embryonic Danmark Stræde. Shortly after the volcanic episode the Kangerdlugssuaq area became the centre of a massive domal upwarping which has been a dominant feature of the land-forms up to the present day. The original surface of the dome has been reconstructed on the basis of topographic and geological evidence to show that it was elliptical in form with a major axis of at least 300 km in length and a height above present sea-level of about 6.5 km. However, subsequent isostatic effects are not considered in deriving these figures. The updoming is estimated to have occurred about 50 m.y. ago.&#x0D; Several kilometres thickness of sediments and lavas were eroded off this dome at an early stage exposing the gneissic core, which still stands in alpine peaks up to about 2.7 km altitude in the central part, and dumping ea. 50000 km3 of sediment on the continental shelf. The erosion was eftected by a radial, consequent drainage system, relicts of which can still be found. Kangerdlugssuaq itself may owe its origin to a tectonic line of weakness formed in response to doming, but there are also good arguments for its being purely erosional. The erosion of the dome was probably fluviatile but all trace of this stage has been obliterated by the subsequent glaciation. In the period between the Eocene and the early Miocene, possibly around 35 m.y. ago, the entire area underwent epeirogenic uplift raising the undeformed parts of the original lava plateau to around 2.5 km above sea-level. At present this plateau is undergoing dissection from the seaward side, but considerable areas are still preserved under thin, horizontal ice-caps.&#x0D; A brief description of the various types of glaciers, an impermanent, ice-dammed lake and the areas of ice-free land is given. In the Pleistocene, the Kangerdlugssuaq glacier was considerably thicker than at the present time and extended far out over the shelf, excavating a deep channel here. Finally some observations on the coastlines are presented.

Discussion

Professor J. S utton asked if the authors regarded the thickness of 9 km as the true thickness, or were they dealing with a succession of tapering flows stacked on each other ? Could they throw any new light on the coastal dyke swarm first described by Wager, whose interpretation had recently been questioned ? Finally, was there in East Greenland any evidence of Tertiary igneous rocks older than the lava flows? Bearing in mind the new ages presented in the paper it was presumably conceivable that the igneous activity so well developed in Western Scotland might have extended into east Greenland to be followed later in the Tertiary by the volcanics so interestingly discussed in this paper. Professor D. T. D onovan asked for elaboration of the view, based as he understood on evidence of rock magnetism, that the great thickness of lavas in the area was erupted over a very short period of time. While the commencement of activity is now well dated as late Paleocene, the Kap Dalton Beds which overlie the lava pile are dated, on molluscan evidence, as middle or even late Eocene (Hassan 1953). Thus on stratigraphical evidence half or more of the Eocene would be available for the eruptive episode. D r C. H. E melevs enquired if there was clear evidence for major normal, coastparallel faulting affecting the basalt lavas but prior to the deposition of the Kap Dalton Formation ? I would agree that at Kap Brewster there is clear evidence of post Kap Dalton

The British Tertiary Igneous Province: Potassium--argon Ages of the Antrim Basalts

Summary Twenty-one K-Ar dates on thirteen lavas from Garron Point, Antrim, Northern Ireland yield a minimum age of 49.9±2.2 My. It would appear that this large thickness (>250 m) of lava was extruded over a period of at most a few million years, in agreement with the results of earlier palaeomagnetic work. There is a correlation between the degree of alteration and apparent age of the samples suggesting that the lavas have lost variable amounts of radiogenic argon.

The stratigraphy and deformation of the Precambrian rocks of the Grænseland area, South-West Greenland

The Grænseland area exhibits a middle Precambrian (Ketilidian) succession of unusually well preserved sediments, basic volcanics, and intrusives. A Ketilidian type lithostratigraphy is established and the evolution of the sedimentary basins is reconstructed. The sedimentation began on a weathered gneiss surface with residual gravel and arkoses. An early carbonate sedimentation led to a severe alteration of the gneiss substratum. Varved pelites and a magnetite-conglomerate with chert pebbles transgressed the earlier deposited sediments and the gneiss substratum; orthoquartzites were thereafter deposited in two basin structures. The deposition of dolomitic shales and pelites appears to indicate progressively increasing depth. Large amounts of graded greywackes, interpreted as turbitides, bear witness of unstable tectonic conditions and a subaqueous tallus indicates nearby fault activity. Filled with greywackes the basins appear to have stabilized, and a comparatively uniform euxenic facies of carbonaceous shales and dolomites with preserved organic remnants prevailed independent of the earlier basins in a period of tectonic quiescence. A considerable thickness of pillow lavas then appears to have been extruded under conditions of quiet subsidence during the euxenic conditions shown by the existence of an anthracite-carbonaceous shale layer and the local facies relations on top of the pillow lavas. A new phase of sedimentation appears to have taken place under conditions of tectonic activity and explosive volcanism. The total thickness of the Ketilidian strata in Grænseland is approximately 4400 m. This succession is compared with other areas of Ketilidian deposits in SouthWest Greenland. The Ketilidian deposits were deformed in two periods of folding, accompanied by thrusting and metamorphism under low greenshist facies conditions. The first deformation is a local drag in incompetent horizons and is possibly related to the tilting and twisting of the basement surface. The second deformation is of regional importance but of very different development depending on the material affected and its position in relation to the sedimentary basins and earlier formed structures. Some areas are virtually undeformed. The basement reacted to the deformations by brecciation and faulting. An analysis of lineations in a thrust zone indicates that the initially formed lineations were twisted and bent towards the direction of tectonic transport. A correlation, based on deformation of metadykes, is attempted with other areas of Ketilidian activity and it is suggested that the second deformation occurred close to 1635 m.y. and corresponds thus to the Sanerutian plutonic episode. The Ketilidian (1800 m.y.? -1500 m.y.) is envisaged as an orogenic cycle of deposition, folding and metamorphism beginning at and ending with major uncomformities. The basement gneisses are shown to contain evidence for two older (pre-Ketilidian) orogenic cycles.

Strong ground motion simulation in the urban area of Catania on the basis of a detailed geological survey

Catania is one of the cities with major seismic hazard in Italy. In history the city was repeatedly hit by destructive earthquakes, e.g., the events of 1 169, 1542 and 1693, all with estimated magnitudes around or above 7. The purpose of our research is the study of site effects and response of soil in the Catania urban area based on synthetic simulations. We have considered three scenarios with earthquakes whose magnitudes range from 5.5 to 7.0 and whose epicentral distances are supposed to be in the range 12-35 km. The subsurface geology of the urban area of Catania is characterized by a marlyclay substratum overlain by lavas, sands and conglomerates. The lava thickness range from a few to over 60 meters, while the thickness of sand terraces ranges from a few to 30 meters. Our study is based on ca. 100 boreholes from which geotechnical and geophysical data were available. We calculated synthetic accelerograms and response spectra at all borehole sites. The results highlight the importance of the subsurface geological conditions, in particular the presence of low velocity layers which enhance seismic loading. On the other hand thick lava layers act as protecting shields against earthquake shaking. Transactions on the Built Environment vol 38 © 1999 WIT Press, www.witpress.com, ISSN 1743-3509

Oxidation and Magnetic Polarity in Single Icelandic Lavas and Dikes

Summary The magnetic polarity and oxidation state have been measured in over five hundred and fifty specimens taken from traverses of fourteen lavas and seven dikes in Eastern Iceland. Oxidation is much higher and more variable in the lavas than in the dikes, suggesting that chemical analyses of dikes are to be preferred to those of lavas as being more representative of the parent magma. Oxidation spectra in each body, within-body polarity consistency, and data from baked sub-basaltic sediments all exclude the existence of self-reversals of magnetic polarity. The data as a whole show no correlation between polarity and oxidation state in the dikes, but a strong correlation exists between the percentage of reversed magnetic polarity specimens and higher oxidation in the lavas. No satisfactory explanation can be given for this observation. The correlation does not change significantly if previous independent oxidation classification systems are applied to the data. In the case of two high oxidation indices, a correlation exists between lava thickness and the oxidation state development.

Thickness of Etnean Lavas

Walker1 has reported observations made on the volcano Etna of the thickness of solid lava flows and the inclination of the slopes on which they lie. He also made estimates of the viscosity of the lava flowing down the slopes of Etna in May 1966, by measuring the thickness and velocity of flow of the lava and the angle of inclination of the slope. The formulae used to determine the viscosity are those for a Newtonian fluid exhibiting laminar flow. Walker sought a relation between the viscosity of fluid lava, the thickness of solid lava and the inclination of the slopes on which the solid lava lies. It seems, however, that such a relation is unlikely because a lava flow having the properties of a Newtonian fluid would continue to flow until no lava at all remained on the sloping surface. Hot lava is observed to flow and cold lava is found to rest on sloping surfaces, however, so we may surmise that flowing lava is not Newtonian in its behaviour, at least as it approaches a fully solid state. Walker's valuable observations enable these questions to be investigated. If the thickness of solid lava flows were determined by the viscosity of the lava when liquid, if this had the properties of a Newtonian fluid, and if the flow were laminar, we should expect to observe a relation between angle of slope, α, and solid thickness, h, of the form where K is a constant. In practice, Walker's observations do not support a relationship of this form but, rather, one of the form where (hν max) is the maximum vertical thickness of lava found on any slope (see Table 1). Now hν sin α is proportional to the shear at the base of the flow caused by the weight of the overlying lava. That (hν max) sin α should be constant for the solid lava flows on Etna suggests that in the final stages of solidification, as the final thickness is determined, the lava is non-Newtonian and approximates in its behaviour to a Bingham plastic2. If the stress acting on a Bingham plastic is smaller than a critical value, which is called the yield stress, no flow occurs, but if the stress acting on it exceeds this value then flow does occur. In the case of lava we may suppose that, as solidification occurs, flow continues until the thickness reaches a value such that, for the slope in question, the shear at the base of the lava caused by the weight of the overlying material becomes smaller than the yield stress, and that at this point flow ceases. If lava flows in the final stages of solidification do behave as Bingham plastics, it is clear that no lower limit to the thickness of a flow is set by this property and so flows may be of any thickness up to the limit set by the yield stress characteristic of the lava concerned and the inclination of the slope on which the lava lies. Walker's observations are consistent with these conclusions if the yield stress of Etnean lava in the final stages of solidification is about 2.5 × 106 dynes/cm2. It follows that, in general, in the case of lavas tilted after their solidification, it is only the maximum thickness of lava at any locality which may supply information about the original slope.

Primary oxidation variation and petrogenesis in a single lava

Oxidation variation between the cooling faces of a single lava has been studied by polished section examination, and Fe2O3: FeO chemical analysis. The oxidation state, which is at a maximum toward the center of the lava, developed during the initial cooling, and has very marked magnetic expression. The Th: U ratio varies in harmony with the oxidation state emphasizing the problem of “resentative” sampling of the body. Examination of thirteen additional bodies suggests that in lavas there exists at least a partial dependence of the oxidation variation development on the lava thickness or interior cooling rate.

Basement Control of Keweenawan and Cambrian Sedimentation in Lake Superior Region

A study of Keweenawan and Cambrian sediments in the Lake Superior region indicates that major structural trends in the basement rocks exerted a prolonged and profound influence upon sedimentation and the development of post-depositional structural features. The major structural elements trend east-west throughout most of northern Michigan, northeast throughout Minnesota and western Ontario, and north-south and east-west near the eastern shore of Lake Superior. Paleocurrent directions show that the outline of the Keweenawan sedimentary basin was essentially parallel with these structural trends. Source areas were near the margins of the present Lake Superior. Subsidence of the basin permitted a great thickness of lava and clastic sediment to accumulate with little or no va iation in the regional slope. Structural contours and isopach lines of the Keweenawan sequence are parallel with paleoslope contours of the Keweenawan basin, indicating that subsidence parallel with basement structural trends was a controlling factor for dispersal patterns and sediment accumulation. Basement control of sedimentation continued throughout most of Cambrian time. Post-depositional structural features such as the Lake Superior syncline and the Keweenaw fault, as well as the present Lake Superior basin, also parallel basement structural trends. It is concluded that resurgent tectonics have been active in the Lake Superior region since pre-Keweenawan time and have exerted a significant effect upon the area to the present.

Basement Control of Keweenawan and Cambrian Sedimentation in the Lake Superior Region: ABSTRACT

A study of Keweenawan and Cambrian sediments in the Lake Superior region indicates that major structural trends in the basement rocks exerted a prolonged and profound influence upon sedimentation and development of post-depositional structural features. The major structural elements trend east-west throughout most of northern Michigan, northeast throughout Minnesota and western Ontario, and north-south to east-west near the eastern shore of Lake Superior. Paleocurrent directions show that the depositional strike and outline of the Precambrian Keweenaw sedimentary basin were essentially parallel with these structural trends. Source areas were located near the margins of the present Lake Superior. Subsidence of the basin permitted great thickness of lava and clastic sedimen to accumulate with little or no variation in the regional slope. Structural contours and isopach lines of the Keweenawan sequence are parallel with paleoslope contours of the Keweenaw basin, indicating that subsidence parallel with basement structural trends was a controlling factor for dispersal patterns and sediment accumulation. Basement control of sedimentation continued throughout most of Cambrian time. Post-depositional structural features such as the Lake Superior syncline and the Keweenaw fault as well as the present Lake Superior basin also parallel basement structural trends. It is concluded that resurgent tectonics have been active in the Lake Superior region since pre-Keweenawan time and have exerted a significant effect upon the area up to the present. End_of_Article - Last_Page 529------------

Upper crustal structure of Iceland

This report contains the results of the seismic measurements made by a Swedish-Icelandic expedition in Iceland during the months of August and September, 1960. This is a continuation of work started a year earlier and is the first detailed investigation of the deeper structure of the lava beds on Iceland. Measurements were made at eight locations, each with a refraction profile from 20 to 41 km long, in order to obtain values on thickness and structure of the lava layer which covers the whole island. The profiles were laid near a line in a southwest-northeast direction across central Iceland. The lava layer was found to consist of three sections with longitudinal wave velocities of 3.7±0.3, 4.95±0.2, and 5.55±0.05 km/sec. The 3.7-km/sec section was found mainly in southwest Iceland, where the other two sections were not found. In north Iceland the 4.95-km/sec section was found near the surface and the 5.55-km/sec section at a depth of about 2 km. The total lava thickness ranges from 1.73 to 4.81 km; it is thin in the southwest and thick in the northern part of Iceland. Below the lava layers, the longitudinal wave velocity is about 6.2 km/sec, increasing to 6.7 km/sec at a depth of about 5 km. Shear waves were clearly recorded on three profiles in north Iceland, but were recorded not at all or only faintly on other profiles.

Basin-Study Approach to Oil Evaluation of Parana Miogeosyncline, South Brazil

Basin-Study Approach to Oil Evaluation of Parana Miogeosyncline, South Brazil

Alexander Logie Du Toit, 1878-1948

Alexander Logie du Toit was born at Newlands, near Cape Town, in the former Colony of the Cape of Good Hope, on 14 March 1878, and died at Pinelands, Cape Town, on 25 February 1948. He was educated at the Diocesan College, Rondebosch, and the South African College, Cape Town, where he obtained the B.A.(Hons.) degree of the University of the Cape of Good Hope, and then proceeded to Glasgow, where he qualified in mining engineering at the Royal Technical College, obtaining the Diploma therein in 1899. He studied geology at the Royal College of Science, London, in 1900-1901. He was lecturer in geology, mining and mine-surveying in the Royal Technical College, Glasgow, and in geology in the University of Glasgow in 1901 and 1902. In 1903 he returned to Cape Town and was appointed Assistant Geologist to the Geological Commission of the Cape of Good Hope. From the date of this first appointment to a few days before his death he devoted himself to the collection of geological data, first in his own land, and later, as opportunity offered, in lands overseas; and, as time went on, he attempted more and more to synthesize this accumulation of facts into a comprehensive picture of the earth’s changes and of the forces that caused them. The mental and physical energy used up by him is incalculable; it poured out from him unceasingly. In the early years of his wrork with the Geological Commission he worked alone in the eastern part of the Cape Colony, covering a large tract of rugged and mountainous country between Herschel in the north and Cala in the south, mapping the various divisions of the Stormberg series and studying in particular the coal horizons of the Molteno beds, the great thickness of Stormberg lavas, and the striking volcanic pipes which penetrate the sediments and lavas of the series. For this work he had no reliable base-maps on which to lay.down geological boundaries; he travelled either on foot or on an ordinary bicycle, with his plane-table carried on his back. No mountain-top was unvisited by him, no valley or ravine left unexplored. The result was a series of field-sheets and geological maps whose detail and accuracy are a source of wonder and envy to the younger men who to-day attempt to ‘revise’ his work with good topographic maps, aerial photographs and motor transport at their command.

The geology and paragenesis of the nickel ores of the Cuniptau Mine, Goward Nipissing District, Ontario

This is a detailed description of a nickel deposit near Goward in the Timagami Provincial Forest 300 miles north of Toronto, Ontario. The general geology of the Cuniptau mine is comparable to that of many other mining areas of that section of Ontario. Lying on the deeply eroded surface of a basement complex is a great thickness of Keewatin lavas. After their extrusion they were folded, faulted, and intruded by peridotite. A long period of alteration and erosion followed, before the final intrusion of many small Keweenawan dikes. It is concluded that the Keweenawan intrusives had no part in the mineralization at Cuniptau mine. This is a case where post-magmatic solutions deposited the copper and nickel sulphides. The important and abundant nickel-bearing sulphide is the secondary nickel sulphide violarite, which may make this nickel deposit one of the first mined in which secondary enrichment has played an important role.