Local Denudation Research Articles

A Compilation of New and Existing Thermochronology Data Concerning the Lhasa Terrane Combined with a Geological Synthesis of the Area

AbstractThe history and geodynamic mechanisms of Cenozoic exhumation and denudation of the Lhasa terrane (LT), southern Tibetan Plateau, remain poorly constrained. Most previous studies investigating the exhumation of the LT have relied on extrapolating interpretations based on a few well‐studied but small areas, which inevitably introduce bias. Here, our compilation of new and published thermochronologic ages are plotted against latitude, longitude, and elevation, to illustrate the distribution of cooling ages across broad regions of the LT. Primary results reveal that (1) the north LT experienced significant exhumation during 80–40 Ma; (2) compared with north LT, exhumation and erosion in the south LT continued after ∼40 Ma; and (3) N–S striking rifting, E–W striking river incision, and thrusts led to continued local denudation of the south LT between 20–5 Ma.

Development Environments and Factors of Subsidence Dolines

This study describes the development environments of subsidence dolines based on literary data (development environments create favorable conditions for the local denudation of superficial deposit and thus, for the development of depressions). Development environments are the inclination of the bearing surface, the secondary porosity of the bedrock, the characteristics of the cover, water influx into the cover, karstwater and groundwater, melting permafrost, and anthropogenic activity. These may become optimal when controlled by various geological, geomorphological, and climatic factors. Development environments may be qualitative (there is doline development in case of its presence) and quantitative (doline development occurs in case of suitable quantitative values). The development environment groups of subsidence dolines are environment groups independent of water level, environment groups dependent on water level, and anthropogenic environment groups. In the case of an environment group independent of water level, surface morphology, cover characteristics, geomorphic evolution, and water supply are determining, while in case of an environment group dependent of water level, subsurface water level and its fluctuations and the characteristics of rainfalls interrupting dry seasons are crucial. Anthropogenic impacts mainly affect doline development through water balance.

The role of frost cracking in local denudation of steep Alpine rockwalls over millennia (Eiger, Switzerland)

Abstract. Denudation of steep rockwalls is driven by rock fall processes of various sizes and magnitudes. Rockwalls are sensitive to temperature changes mainly because thermo-cryogenic processes weaken bedrock through fracturing, which can precondition the occurrence of rock fall. However, it is still unclear how the fracturing of rock together with cryogenic processes impacts the denudation processes operating on steep rockwalls. In this study, we link data on long-term rockwall denudation rates at the Eiger (Central Swiss Alps) with the local bedrock fabric and the reconstructed temperature conditions at these sites, which depend on the insolation pattern. We then estimate the probability of bedrock for failure through the employment of a theoretical frost cracking model. The results show that the denudation rates are low in the upper part of the NW rockwall, but they are high both in the lower part of the NW rockwall and on the SE face, despite similar bedrock fabric conditions. The frost cracking model predicts a large difference in cracking intensity from ice segregation where the inferred efficiency is low in the upper part of the NW rockwall but relatively large on the lower section of the NW wall and on the SE rock face of the Eiger. We explain this pattern by the differences in insolation and temperature conditions at these sites. Throughout the last millennium, temperatures in bedrock have been very similar to the present. These data thus suggest the occurrence of large contrasts in microclimate between the NW and SE walls of the Eiger, conditioned by differences in insolation. We use these contrasts to explain the relatively low denudation rates in the upper part of the NW rockwall and the rapid denudation in the SW face and in the lower part of the NW rock face where frost cracking is more efficient.

Was Alexandria (Egypt) Destroyed in A.D. 365? A Famous Historical Tsunami Revisited

Abstract Ammianus Marcellinus, a fourth-century writer, reported that after an earthquake, on 21 July 365, the sea retreated and then flooded numerous coasts, among them Alexandria (Egypt) and Methoni (southwest Greece). Several other ancient authors seem to mention this event as a “universal earthquake.” The inferred tsunami is usually assigned to reactivation of a fault in the Hellenic (Aegean) Arc, derived from an up to 9 m seismic uplift of Crete. Modeling of this uplift revealed an 8.5+ magnitude earthquake and a tsunami that affected most of the Eastern Mediterranean. For Alexandria, a flooding wave arrival is predicted, and marginal impacts are not excluded because of the topography of the ancient town. On the other hand, ancient sources lead to contradictory results, from no damage to devastation, but new historical evidence indicates that many of the historical reports of the critical period are biased by religious and political ideas, and the Ammianus description was questioned. Hence, for Alexandria there exist three scenarios: major destruction, marginal damage, and no damage by the 365 tsunami. To shed light to this debate (1) ancient sources were analyzed in view of new evidence for their significance, (2) possible impacts of a tsunami in the town’s infrastructure were discussed, and (3) possible impacts of a major destruction were investigated in the framework of the well-known ecclesiastical and civil history of Alexandria. The main conclusions of this study are that (1) no significant tsunami destruction is likely for Alexandria, in agreement with sedimentary evidence, and no major tsunami runup for Methoni; (2) a major earthquake in 365 is likely offshore Crete; and (3) it is inferred that Ammianus brings together two tsunamis, a local slump offshore that produced water retreat and then flooding and local denudation in the eastern Nile Delta, and a second tsunami generated by a fault offshore Crete or in the Ionian and the Adriatic Sea.

Prevalence of Power Law Profiles in Passive Margin Escarpments

An analysis of elevation data from several great escarpment regions across the globe revealed a prevalence of inverse power law forms among the escarpment profiles. The best fit power law exponent varies among profiles and has a global median value of 0.9 and standard deviation of 1.8. The power law form is consistent with the shape of a detachment‐limited escarpment that is retreating headward while maintaining a constant shape. Such a constant‐shape evolution requires the local denudation rate to be equal to the product of escarpment retreat rate and local slope. The available basin‐averaged denudation rate data from several great escarpment regions are consistent with this constraint, and this allows estimation of the recent retreat rates of the escarpments within the constant‐shape assumption.

Morphological controls on the dynamics of carbonate landscapes under a mediterranean climate

AbstractThe influence of the morphological setting on the denudation of carbonate landscapes and the respective contributions of mechanical and chemical weathering processes are still debated. We have addressed these questions by measuring 36Cl concentrations in 40 samples from the Luberon mountain, SE France, to constrain the denudation of various landscape elements. We observe a clear contrast between the local denudation rates from the flat summit surface, clustered around 30 mm/ka, and the basin‐average denudation rates across the flanks, ranging from 100 to 200 mm/ka. This difference highlights the transient evolution of the range, whose topography is still adjusting to previous uplift events. Such a pattern also suggests that carbonate dissolution is not the only driver of denudation in this setting, which appears to be significantly controlled by slope‐dependent processes.

Conodont color alteration index and upper Paleozoic thermal history of the Amazonas Basin, Brazil

The conodont color alteration index (CAI) was determined in elements from core samples of the Frasnian Barreirinha Formation (one well) and of the Pennsylvanian–Permian Tapajós Group (twenty three wells and one limestone quarry) in the Amazonas Basin. The thermal history of the basin is analyzed using the CAI value distribution represented in maps and stratigraphic sections through correlation schemes, and in conjunction with previously published data. The pattern of palaeotemperatures for CAI values of 1.5–3 is coincident with organic matter maturation under a sedimentary overburden providing diagenetic conditions in the oil/gas window. Locally, conodonts show metamorphism (CAI value of 6–7) in relation to the intrusion of diabase bodies in beds including high geothermal gradient evaporites. Microtextural alteration on the surface conodonts commonly shows several types of overgrowth microtextures developed in diagenetic conditions. Locally, recrystallization in conodonts with a high CAI value is congruent with contact metamorphism in relation to Mesozoic intrusions. The CAI values of 1.5 or 2 observed close to the surface in several areas of the basin may be interpreted in relation to a high thermal palaeogradient derived from the magmatic episode or/and to the local denudation of the upper part of the Paleozoic succession prior to this thermal event.

The long-term denudation rate of granitic regolith in Qinhuangdao, North China determined from the in situ depth profile of the cosmogenic nuclides 26Al and 10Be

This study quantifies the surface denudation rate of granitic regolith via the application of the in situ cosmogenic 26Al and 10Be depth profile in China. The concentration ranges of 26Al and 10Be in the quartz along the ~3-m granitic regolith profile in Qinhuangdao are (4.9–23.1) × 105 and (2.3–36.6) × 104 atoms/g, respectively. With the exception of the surface sample, both 26Al and 10Be concentrations decrease exponentially with sample depth. The Chi-square best-fitting results revealed a total denudation rate of ~9 m/Ma averaged over a 103–105 a timescale, which is lower than the values observed in global granitic outcrops. Compared with global datasets, the flat terrain due to the lack of tectonic activities is most likely the dominant factor that controls the local denudation process. The surface sample offsets from the theoretical cosmogenic nuclide distribution implies that the denudation rate from river basin sediment could be overestimated because of the bioturbation in the surficial soil layer.

Landscape evolution of a bedrock peneplain on the southern Tibetan Plateau revealed by in situ-produced cosmogenic 10Be and 21Ne

Low-relief bedrock surfaces that occur at high altitude are a common feature of Cenozoic mountain belts and have often been used to infer a significant amount of rock uplift after their generation at low elevation. The timescale over which such surfaces can be preserved at high elevation and the rate at which they are modified by weathering and erosion are poorly known. Here we use cosmogenic 10Be and 21Ne to quantify the landscape evolution of a bedrock peneplain in southern Tibet that occurs at an altitude of ~5300m. The peneplain is developed in Cretaceous granitoids and Jurassic metasediments of the northern Lhasa block (90°E, 31°N) and originally had a minimum extent of ~150km east–west and ~75km north–south. It has been dissected by small rivers that generated a few hundred meters of relief and formed additional bedrock surfaces of limited extent at lower elevation. Local denudation rates for the peneplain and the lower bedrock surfaces – based on 10Be concentrations in grus samples and amalgamated quartz clasts – cluster between 5 and 11mMa−1 (mean=8.1mMa−1) and are thought to be representative for the long-term rate of downwearing of these surfaces. Samples from bedrock outcrops and bedrock blocks yield more variable rates (3–20mMa−1), which partly overestimate the long-term lowering rate, presumably due to block tilting and bedrock inhomogeneity. Spatially averaged 10Be denudation rates for small river catchments range from 9 to 16mMa−1 (mean=11.8mMa−1) and are only slightly higher than the local denudation rates. Hence, the incision and widening of valleys proceeds at low rates, which demonstrates that the landscape of the peneplain region is remarkably stable. The combined 21Ne and 10Be data in a subset of the samples suggest that the bedrock surfaces have experienced a simple exposure history without periods of burial. Thus, our data do not provide any evidence for extended periods of shielding by ice during past glaciations, which is consistent with the absence of erratic boulders and moraines in the peneplain region.

Dating Pleistocene aeolian landforms in Hungary, Central Europe, using in situ produced cosmogenic 10BE

In the Western Pannonian Basin the widespread occurrence of ventifacts and large-scale deflation features indicate strong wind activity during the Quaternary. Pleistocene glaciations are probably the most important periods of wind erosion. However, age of the wind-polished rock surfaces exposed on different geomorphic horizons has remained unknown so far, although they can provide time constraints of landscape evolution. Measurements of 10Be concentrations along depth profiles of exposed wind-facetted rocks allow deriving local denudation rates of 3.46–3.88 m/Ma and exposure ages as old as 1.5 Ma. Regional denudation, which occurred mainly via deflation of the loose sediments, varies between 40 and 80 m/Ma. This study provides evidence that aeolian erosion in continental, periglacial areas of Central Europe played an important role in Quaternary landscape modification.

Determining the growth rate of topographic relief using in situ-produced 10Be: A case study in the Black Forest, Germany

Abstract To determine how topographic relief in mountainous regions evolves through time we present a new approach that uses in situ -produced cosmogenic 10 Be to quantify (1) spatially averaged denudation rates of small watersheds and (2) local denudation rates of the ridge crests bounding these basins. The technique is applied to two catchments in the Black Forest, a forested mountain range with a local relief of a few hundred meters, which is typical for ranges in central Europe. Both the Acher and the Gutach catchments expose predominantly Carboniferous granite, and only minor amounts of high-grade gneiss and Triassic sandstone. The latter occurs on ridges defining the eastern boundaries of the catchments, above a regional unconformity. In the Acher and northern Gutach watersheds denudation rates of subcatchments derived from 10 Be concentrations in stream sediment range from 52 to 87 mm/ka and 59 to 91 mm/ka, respectively. In contrast, grus samples from the ridge crests bounding both watersheds yield lower denudation rates of 34 to 59 mm/ka. The differences in denudation rates for sample pairs from individual subcatchments and adjacent ridge crests reveals that topographic relief is growing at a mean rate of 24 ± 12 mm/ka (with the exception of the flat southwestern part of the Gutach catchment, where catchment-wide denudation rates are similar to the rate of ridge crest lowering). The inferred rates of denudation and relief growth are consistent with erosion rates calculated from the known thickness of Triassic to Lower Jurassic sediments, which were once present above the regional unconformity but have been largely eroded during the exhumation of the Black Forest. The onset of exhumation ∼ 19 Ma ago is constrained by thermal modelling of apatite fission track data, which suggest a cooling rate of ∼ 3 °C/Ma. Combined with a geothermal gradient of 30 to 40 °C/km this cooling rate yields an average exhumation rate of 75–100 mm/ka for the modelled apatite fission track data, which is comparable to spatially averaged denudation rates derived from cosmogenic 10 Be. Our new approach may help to determine whether tectonically active mountain ranges are in a topographic steady state, in which rates of rock uplift and denudation are equal, or if such a dynamic equilibrium has not yet been attained.

Conduit properties and karstification in the unconfined Floridan aquifer.

Exchange of water between conduits and matrix is an important control on regional chemical compositions, karstification, and quality of ground water resources in karst aquifers. A sinking stream (Santa Fe River Sink) and its resurgence (River Rise) in the unconfined portion of the Floridan Aquifer provide the opportunity to monitor conduit inflow and outflow. The use of temperature as a tracer allows determination of residence times and velocities through the conduit system. Based on temperature records from two high water events, flow is reasonably represented as pipe flow with a cross-sectional area of 380 m2, although this model may be complicated by losses of water from the conduit system at higher discharge rates. Over the course of the study year, the River Rise discharged a total of 1.9 x 10(7) m3 more water than entered the River Sink, reflecting net contribution of ground water from the matrix into the conduit system. However, as River Sink discharge rates peaked following three rainfall events during the study period, the conduit system lost water, presumably into the matrix. Surface water in high flow events is typically undersaturated with respect to calcite and thus may lead to dissolution, depending on its residence time in the matrix. A calculation of local denudation is larger than other regional estimates, perhaps reflecting return of water to conduits before calcite equilibrium is reached. The exchange of matrix and conduit water is an important variable in karst hydrology that should be considered in management of these water resources.

In Vivo Evaluation of the Hydrolyser Hydrodynamic Thrombectomy Catheter

The authors evaluated a 7-F double-lumen thrombectomy catheter (Hydrolyser) in vivo. To evaluate efficacy, thrombectomy was performed 1, 4, or 8 days after local denudation in peripheral arteries (n = 18) and veins (n = 29) of nine goats. To evaluate safety, the reaction of the vessel wall to a functioning and nonfunctioning Hydrolyser catheter was evaluated in the peripheral arteries and veins of three goats 10 days after the procedure. Reopening was achieved in all vessels with residual thrombus in 11% of arteries (two of 18) and 55% of veins (16 of 29). Slight intimal thickening was observed, but no difference was seen between the passage of a functioning versus nonfunctioning catheter. The Hydrolyser device can remove intravascular thrombus up to 8 days after induction. There was no difference in vessel wall reaction after the passage of a functioning and nonfunctioning catheter.

Neurotoxicity and pharmacokinetics of ventriculolumbar perfusion of methyl 6-[3-(2-chloroethyl)-3-nitrosoureido]-6-deoxy-alpha-D-gluco-pyranoside (MCNU) in dogs

Ventriculolumbar perfusion of methyl 6-[3-(2-chloroethyl)-3-nitrosoureido]-6-deoxy-alpha-D-glucopyranoside (MCNU), a water soluble nitrosourea with log P -0.71, may be efficacious in the treatment of subarachnoid dissemination of malignant glioma. We used 2 dogs to study the neurotoxicity and pharmacokinetics of MCNU. MCNU (1 mg), dissolved in 10 ml of artificial CSF, was administered via the right lateral ventricle during a period of 18 to 42 min and the CSF was drained by lumbar puncture. The perfusion was repeated once a week for 10 consecutive weeks. No neurological and systemic symptoms were noted after perfusion. Histological examination of the brain and spinal cord showed local denudation of the ependyma and local subependymal spongy degeneration and gliosis in the lateral ventricle into which MCNU was administered in one dog and local denudation of the ependyma in the other. When administration was over a period of 21 to 38 min, the MCNU concentration in the lumbar CSF peaked at 11.11 to 50.67 micrograms/ml, in 28 to 78 min. The area under the drug concentration-time curve (AUC) was 1152 micrograms x min/ml on average, significantly larger than that of ACNU. The elimination phase followed linear kinetics and the half-time was 41.1 min on average, significantly longer than that of ACNU. These findings suggest that ventriculolumbar perfusion of MCNU may be effective in the treatment of subarachnoid dissemination of malignant glioma notwithstanding some local histological changes.

Capacity and kinetics of SLD repair in mouse tongue epithelium

The effect of dose fractionation on the radiation response of mouse tongue epithelium was quantified in fractionation protocols involving 1, 3, 4, 5 and 10 fractions, separated by at least 4 h. Fractionated irradiation was given either to the whole snout by 300 kV X-rays or locally to the tongue using 25 kV X-rays. Each protocol was terminated by a final local top-up dose (25 kV X-rays) of 5 Gy. The frequency of complete local denudation within the test area was used as the quantal end point. The kinetics of repair of sublethal damage was studied by snout irradiation with four equally spaced fractions, delivered at intervals of 35, 60, 90, 480 or 540 min, again followed by a local top-up dose of 5 Gy. The linear-quadratic model gave a satisfactory fit to the data [40] with the exception of the four fraction/30-h data, suggesting cell cycle effects in this schedule. Analysis of the results with different two-step methods and with direct analysis [37] yielded similar results. The α β ratio was determined to be ∼11 Gy (direct analysis: 11.6 Gy with 95% confidence limits of 8.1 and 16.4 Gy) and T 1 2 was found to be 46 min (35–69 min). Both these values are in the range described for other acutely responding rodent tissues.

Late Paleozoic Structural Evolution of Permian Basin: ABSTRACT

The Permian basin of West Texas and New Mexico is one of the premier hydrocarbon provinces of the world; nonetheless, little regional subsurface structural information about it has been published. Mapping at 1:250,000 on the Ellenburger horizon (Lower Ordovician), compiled for the Tectonic Map of Texas, discloses the overall geometry of Paleozoic deformation in the area. The southern Permian basin is underlain by the NNW-trending Central Basin disturbed belt of Wolfcamp age (Lower Permian), the deep Delaware basin to its west, and the shallower Midland basin to its east. The disturbed belt is highly segmented with zones of left-lateral offset. Major segments from south to north are: the Puckett-Grey Ranch zone; the Fort Stockton uplift; the Monahans transverse zone; the Andector ridges and the Eunice ridge; the Hobbs transverse zone; and the Tatum ridges, which abut the broad Roosevelt uplift to the north. East-west compression is inferred, with shortening increasing from the Tatum ridges south to the Fort Stockton uplift. The segment boundaries and transverse elements are inferred zones of strike-slip faulting. These fault zones extend both southeast and west of the disturbed belt into discrete strike-slip faults with local uplifts in compressive bends (such as the Big Lake uplift). The Midland basin is much shallower than the Delaware basin, and the uplift-to-basin transition is gradual. A belt of subtle domes and anticlines, extending northeast from Andrews County, overlies a major basement discontinuity (the Grenville Front). The disturbed belt may have originated along rift zones of either Precambrian or Cambrian age. The extent of Lower and Middle Pennsylvanian deformation is unclear; much of the Val Verde basin-Ozona arch structure may have formed then. The main Wolfcamp deformation overthrust End_Page 474------------------------------ the West Texas crustal block against the Delaware block, with local denudation of the uplifted edge and eastward-directed backthrusting into the Midland basin. Later in the Permian, the area was the center of a subcontinental bowl of subsidence--the Permian basin proper. The disturbed belt formed a pedestal for the carbonate accumulations which created the Central Basin platform. The major pre-Permian reservoirs of the Permian basin lie in large structural and unconformity-bounded traps on uplift ridges and domes. Further work on the regional structural style may help to predict fracture trends, to assess the timing of oil migration, and to evaluate intrareservoir variations in the overlying Permian giant oil fields. End_of_Article - Last_Page 475------------

Geological Investigation of the Niigata Oilfield

General stratigraphy and palaeontology on the Niigata Oilfield region are described and discussed on the compiled basis of the recent geological and geophysical survey with the application of the knowledge of oceanography, palaeoecology and sedimentlogy.The writer proposes the new stage scheme for this region, they are, from lower to upper, the Tsukawan, the Teradomarian, the Shiiyan, the Nishiyaman, the Haizumean, the Yamayan, the Ogunian and Oyaman. Fig. 1. shows the columuar section of the Tsukawan. Fig. 2. is the isopach map of the shiiya formation. Here, the writer gives a new idea on the developmet of the geologic structure of this region. That is, although there are some differences in degree on scale, on age and in place, the deposition, local denudation, folding and faultng are carried on continuouously and progressively, accompanied with the upheaval and subsidence of the basement bl_??_ck and igneons action. Also at present, it is carrying on. This idea is shown diagramatically in Fig. 3, in which direction of arrow shows one component of the four-dimensioned vector including time factor. This phenomenon, the word of "evolutional cnange" being proposed for it, is believed to be the true attitude of the earth's crust.

About Polar Glaciation &c.

Summary Evaporation and condensation, atmospheric and oceanic circulation are caused by unequal local temperatures. Rivers and land-glaciers alike result from atmospheric circulation, and from local condensation, and they flow for the same reasons at different rates. The existing Arctic current is part of ocean circulation, caused by unequal polar and equatorial temperatures. That current is a conspicuous fact. It is far larger and more powerful than any existing river or ice flow on land. It is more than three thousand miles long, and it is very broad; it moves vast fragments of the largest existing land-glaciers, and great sheets of thick polar sea-ice, at great speed. It lowers the perpetual snow-limit where it flows, and it there modifies climate and all that depends on climate. Within an area equal to that of India, in Greenland it increases local condensation, and snow-flake's, and snow-falls, and ice flows and rivers; and so it increases local denudation on shore while it works on the shallows. Ice rafts in the ocean-stream carry drift southwards; and the water which drags these loaded rafts over shallows and makes them drop boulders, also rolls and packs mud and shingle and builds a delta in the sea. This kind of polar “glaciation” and deposition of “drift,” caused directly and indirectly by one of the northern polar currents, cannot be denied. The agent is a true cause at work; and the work ought to be like that which I saw in Russia in 1873. Where a sedimentary rock exists there water has been; and the drift-plains of Russia are spread upon sedimentary series little disturbed. That part of the earth's crust has been up and down many times without breaking much. If glacial periods, due to astronomical or other causes, have in fact increased evaporation and condensation, ice-flows, and rivers to any given extent, then polar currents must have gained power during these periods, because movements in air and ocean result from unequal local temperatures, on which also depend the local growth of ice on land.

On the Red Chalk of Hunstanton

N ot far from the apex of the angle which the Wash, opening out into the German Ocean, forms on the western coast of Norfolk, is situated a cliff of about a mile in length and 50 or 60 feet in height, on which, at its greatest elevation, is erected the Hunstanton Lighthouse. This headland, which gradually rises from the low ground on the north, and finally sinks towards the south through the effect of local denudation, is remarkable, even when viewed from a distance, from the circumstance that its face is marked by three parallel coloured bands, slightly inclined, and cropping out in succession on the surface soil, of which bands the uppermost is white, the next bright red, and the lowest yellow, each division being sharply defined, without any intermingling of tints at the lines of contact. A close inspection shows that the highest stratum, the white, consists of a hard calcareous substance, compact in texture, and much shattered and fissured, originally deposited in such a manner that its materials were arranged in definite layers, two of which ( a, b ), those forming the base, are represented in the annexed section drawn to scale. The first of these ( a ), in thickness about 2 feet 6 inches, is noticeable for the presence of an enormous quantity of fragments of Inocerami dispersed throughout its whole extent, and which under the influence of weathering impart to this portion of the cliff a jagged and rough appearance. Its characteristic fossils are spines of Cidaris

The Ironstone-Formation of the Forest of Dean; with a Sketch of the General Geology and Industrial History of the District

The coal-measures repose conformably on a series of grit-beds, all more or less charged with oxide of iron, and measuring together about 500 feet in thickness. In some places a bed of limestone intervenes between the lowest bed and those above, but the general section, in descending order, is as follows:—1. Coarse red grit-stone, called “The Miner's Farewell Rock.”2. Light red sandstone, with layers of variegated marls, which, although partly indurated in the bed, fall to pieces by exposure to the air.3. Fine-grained quartzose grit, much charged with iron in the middle beds, constituting the “Sandstone Mine Formation.” In this group there are two thin beds of coarse conglomerate, or pudding-stone.It would be impossible for me to enter into any adequate description of this most important part of the Forest geology, without extending this article to an undue length. The following summary, therefore, must suffice, in the present instance; although I purpose describing the coalfield, which has special interest—geological as well as industrial—on another occasion.If the ordnance geological sheet No. XLIII. S.E. be examined, with the horizontal sections Nos. 15 and 16, a very good notion of this coal-basin may be obtained, although not too much dependence is to be placed, practically, on the position of the lines marking the crop of the several veins. Indeed, to lay down the line of crop accurately, in many places where there are no workings, is impossible, from the thickness of the over-burden or soil: besides which, the theoretical lines invariably require to be shifted, from the occurrence of minor faults and local denudation.