Unaltered Material Research Articles

Mineralogy and geochemistry of some “so-called” paleosols from Mt. Vulture volcano (southern Italy)

Three tephra beds with suspected paleoweathering effects from the Mt. Vulture volcano zone (Potenza, Italy) were studied. Grain-size, chemical and mineralogical analyses, and SEM observations were performed to estimate the stage of weathering. This study reveals the difficulties in the study of early stages of weathering of pyroclastic rocks. The results point out the existence of four successive stages or processes: (a) pre-depositional stage (pre- or eruptive features of pyroxenes, quartz and phlogopite); (b) depositional stage (persistence of grain-size distribution similar to unaltered materials; low clay fraction content); (c) circulating water stage (in the lower bed) (more altered pyroxenes with depth; smectite-calcite-Mn-hydroxides association; increase in consistence with depth); and (d) weathering stage (decrease of allophane and amorphous silico-alumina with depth; release of alkali ions). The existence of these overlapping processes produces variations of grain size, mineralogy and chemistry through each bed (paleosol) that hinders the obtainment of geochemical balances or calculations.

Effect of molecular architecture on microstructural characteristics in some polysiloxaneimide multiblock copolymers

AbstractEfforts to correlate molecular characteristics with microstructural dimensions in microphase‐separated diblock and triblock copolymers have been very successful, resulting in relationships that can be utilized to design materials with a specific microstructure and, consequently, with particular thermomechanical properties. However, similar efforts in the arena of multiblock copolymers have not been nearly as extensive, despite the increasing interest and diversity of this class of materials. In the present work, energy‐filtered electron microscopy (EFEM) and small‐angle neutron scattering (SANS) are used in a complementary fashion to probe the phase behavior of a series of three polysiloxaneimide (PSI) multiblock copolymers with different molecular architectures. Despite their relatively short segment lengths, all three materials exhibit signs of microphase separation at ambient temperature. SANS data are obtained from chemically unaltered materials and are subsequently interpreted with the Teubner‐Strey model for microemulsions. Resultant microstructural dimensions are in good agreement with those measured from EFEM micrographs. Additional insight into the intramolecular sequencing of each copolymer is obtained from scaling relationships.

The validity of whole-rock geochemistry in the study of the oceanic crust: a case study from ODP Hole 504B.

Abstract Attempts to interpret the geochemistry of the oceanic crust are constrained by the representative nature, quality, and amount of material recovered from an individual site. The most effective sampling method has been that of continuous coring while drilling, although the amount of material recovered from a single hole can vary with depth from 0 to 100%, and is often, though not necessarily, low. Observations suggest there is inevitably a biasing towards the recovery of unaltered material. DSDP/ODP Hole 504B has been successfully drilled in a series of stages and a 1500 m section of the oceanic crust has been sampled. The core recovery in Hole 504B is, however, generally poor; consequently the study of both igneous and alteration processes at this site is limited. An alternative to this scenario is offered by down-hole geochemical (nuclear) measurements. The nuclear responses provide a limited but near-continuous geochemical dataset within this hole. The derived chemo-stratigraphy correlates well with that based upon conventional geophysical measurements. Alteration has played an important role in producing the observed chemical signatures and may partly explain the poor core recovery within the hole. Downhole nuclear measurements in the ocean crust provide a novel geochemical dataset in the study of both primary and secondary processes. This information must be integrated with lithological, petrological and geophysical data to produce the most complete appraisal yet of the oceanic crust.

Curriculum Policy as Compensatory Legitimation? A View from the Periphery

Abstract The continuing debate on the relevance and imposition of ‘Western theories’ for explaining educational policy in the Third World is fascinating on a rhetorical level but lacking in the actual ‘testing’ of such theories in a cross‐national context. Responding to the general debate, and to a particular paper by Hans Weiler included in this issue of the Oxford Review of Education, on curriculum reform in West Germany, this paper explores the utility of the construct of ‘compensatory legitimation’ for the comparative study of curriculum policy. After demonstrating the limits of existing compensatory strategies for explaining the curriculum policy of Zimbabwe, a new application for the theoretical construct is advanced for post‐colonial states. The specific argument of this paper is that socialist curriculum policy, independent of actual curriculum practice, serves as a powerful vehicle for the legitimation of the state in post‐colonial societies in the face of unaltered (capitalist) material conditions.

The sedimentary cycle of the boron isotopes

Abstract Marine sediments contain two isotopically distinct components: a non-desorbable fraction with δ11B between −4.3 and +2.8 per mil (n = 10) and a desorbable component with δ11B between 13.9 and 15.8 per mil (n = 6). The adsorption coefficient, K, for the uptake of B from seawater by fluvial suspended material (Mississippi) has an experimentally determined value of 1.54 ± 0.05. The associated isotope fractionation factor, α, is 0.974 ± 0.003. Empirical values for K, determined from the analysis of marine sediments (n = 6), were between 3 and 4. The amount of B adsorbed onto fluvial suspended material during estuarine mixing is about 9 × 109 moles/yr. Based on pore water data, adsorption experiments and comparative size fraction analyses (suspended sediments from the Mississippi River vs. bottom deposits from the Delta) there is no evidence for the incorporation of B into detrital sediments at low temperature. However, the high B content of Bauer Deep metalliferous sediments must be due to incorporation of seawater B during formation of authigenic silicates. The δ11B of these minerals is 2 ± 3 per mil. Hydrothermally altered sediments from DSDP Hole 477, Guaymas Basin, Gulf of California have variable B contents, from 33 ppm, similar to the unaltered detritus, to 1.2 ppm in the recrystallized material. The latter has δ11B as low as −9.0 per mil, substantially lower than the unaltered material. Hydrothermal solutions collected from vents adjacent to the hole have boron contents elevated by about a factor of 4 relative to seawater and δ11B between 16.5 and 23.2 per mil. The B mobilized from the sediments is isotopically fractionated with the fluids being preferentially enriched in the heavy isotope. Analysis of an oxisol profile developed over granite in the Guyana Shield showed that boron is partially mobilized during weathering with an isotopic offset of 2.5 per mil between bedrock and soil. The observed enrichment of B in shales relative to igneous rocks does not occur during weathering or during exposure to seawater at low temperature. Incorporation occurs only during burial diagenesis at temperatures greater than about 60°C. However, the enrichments cannot be attained during a single cycle of primary weathering and burial but must be cumulative over many cycles.

Boron cosmochemistry

Boron, sulfur, silicon, and sodium abundances have been measured in 50 pieces from 28 chondritic meteorites. Thirty-one of these samples were carefully selected and prepared to avoid composition changes from contamination or alteration in the terrestrial environment. Boron and sodium abundances define two domains within C2M carbonaceous chondrites: one contains 8.5 B10 6 Si and 0.044 NaSi and the other 25 B10 6 Si and 0.021 Na10 6 Si . It is proposed that these differences are the result of element redistribution within C2M chondrites in response to low-temperature hydrous processes. Petrologic type 5 and 6 chondrites are also composed of two types of material, one has 3.5 B10 6 Si and the other 11 B10 6 Si . The mass weighted average of the boron concentration in high-petrologic-type ordinary chondrites is indistinguishable from the measured abundances in petrologic type 3 and 4 ordinary chondrites. We suggest that the compositional differences within petrologic types 5 and 6 are the result of high-temperature modifications of materials that had boron abundances like those now observed in the low petrologic types. We assumed that the redistribution of these elements was closed on the scale of the mass of the available meteorites, and determined the abundances in unaltered material by calculating the mass weighted average of the measured abundances in all the samples of one chondrite type. We used these averages to calculate boron depletion factors in chondrite types. The factors are C2 = 0.62, C3 = 0.31, and ordinary chondrites= 0.34. These are similar to the sulfur depletion factors in the same types of meteorites. The agreement suggests that boron, like sulfur, had a nebular condensation temperature at the lower end of the range of moderately volatile elements. Within the context of this interpretation, the solar abundance of boron is 21 B10 6 Si —the concentration in the interior piece of the C-1 carbonaceous chondrite Orgueil.

Failure modes of InGaAsP/InP lasers due to adhesives : Mitsuo Fukuda, Osamu Fujita and Genzo Iwane. IEEE Trans. Components Hybrids Mfg Technol.CHMT-7 (2), 202 (1984)

Prominent macroscopic sedimentary laminations, consisting of mm- to cm-thick alternating well-sorted but poorly mixed silicate and metal-rich layers cut by faults and downward penetrating load structures, are prevalent in the Isheyevo (CH/CBb) carbonaceous chondrite. The load structures give the up direction of this sedimentary rock that accumulated from in-falling metal- and silicate-rich grains under near vacuum conditions onto the surface of an accreting planetesimal. The Isheyevo meteorite is the end result of a combination of events and processes that we suggest was initiated by the glancing blow impact of two planetesimals. The smaller impactor was disrupted forming an impact plume downrange of the impact. The components within the plume were aerodynamically size sorted by the nebular gas and swept up by the impacted planetesimal before turbulent mixing within the plume could blur the effects of the sorting. This plume would have contained a range of materials including elementally zoned Fe-Ni metal grains that condensed in the plume to disrupted unaltered material from the crust of the impactor, such as the hydrated matrix lumps. The juxtaposition of hydrated matrix lumps, some of which have not been heated above 150°C, together with components that formed above 1000°C, is compelling evidence that they were swept up together. Sweep-up would have occurred as the rotating impactor moved through the plume producing layers of material: the Isheyevo sample thus represents material accumulated while that part of the rotating planetesimal moved into the plume. Vibrations from subsequent impacts helped to form the load structures and induced weak grading within the layers via kinetic sieving. Following sweep-up, the particles were compacted under low static temperatures as evidenced by the preservation of elementally zoned Fe-Ni metal grains with preserved martensite α2 cores, distinct metal-metal grain boundaries, and metal-deformation microstructures. This meteorite provides evidence of gentle layer-by-layer accretion in the early Solar System, and also extends the terrestrial sedimentary source-to-sink paradigm to a near vacuum environment where neither fluvial nor aeolian processes operate.

Reliability of gate metallization in power GaAs MESFETS : K. Katsukawa, Y. Kose, M. Kanomori and S. Sando. Proc. IEEE Reliab. Phys. Conf. 59 (1984)

Prominent macroscopic sedimentary laminations, consisting of mm- to cm-thick alternating well-sorted but poorly mixed silicate and metal-rich layers cut by faults and downward penetrating load structures, are prevalent in the Isheyevo (CH/CBb) carbonaceous chondrite. The load structures give the up direction of this sedimentary rock that accumulated from in-falling metal- and silicate-rich grains under near vacuum conditions onto the surface of an accreting planetesimal. The Isheyevo meteorite is the end result of a combination of events and processes that we suggest was initiated by the glancing blow impact of two planetesimals. The smaller impactor was disrupted forming an impact plume downrange of the impact. The components within the plume were aerodynamically size sorted by the nebular gas and swept up by the impacted planetesimal before turbulent mixing within the plume could blur the effects of the sorting. This plume would have contained a range of materials including elementally zoned Fe-Ni metal grains that condensed in the plume to disrupted unaltered material from the crust of the impactor, such as the hydrated matrix lumps. The juxtaposition of hydrated matrix lumps, some of which have not been heated above 150°C, together with components that formed above 1000°C, is compelling evidence that they were swept up together. Sweep-up would have occurred as the rotating impactor moved through the plume producing layers of material: the Isheyevo sample thus represents material accumulated while that part of the rotating planetesimal moved into the plume. Vibrations from subsequent impacts helped to form the load structures and induced weak grading within the layers via kinetic sieving. Following sweep-up, the particles were compacted under low static temperatures as evidenced by the preservation of elementally zoned Fe-Ni metal grains with preserved martensite α2 cores, distinct metal-metal grain boundaries, and metal-deformation microstructures. This meteorite provides evidence of gentle layer-by-layer accretion in the early Solar System, and also extends the terrestrial sedimentary source-to-sink paradigm to a near vacuum environment where neither fluvial nor aeolian processes operate.

Organic geochemistry of Deep Sea Drilling Project sediments from the Gulf of Calofornia—hydrothermal effects on unconsolidated diatom ooze

The effects of intrusive thermal stress have been studied on a number of Pleistocene sediment samples obtained from Leg 64 of the DSDP-IPOD program in the Gulf of California. Samples were selected from Sites 477, 478 and 481 where the organic matter was subjected to thermal stress from sill intrusions. For comparison purposes, samples from Sites 474 and 479 were selected as representative of unaltered material. The GC and GC-MS data show that lipids of the thermally unaltered samples were derived from microbial and terrestrial higher-plant detritus. Samples from sill proximities were found to contain thermally-derived distillates and those adjacent to sills contained essentially no lipids. Curie point pyrolysis combined with GC and GC-MS was used to show that kerogens from the unaltered samples reflected their predominantly autochthonous microbial origin. Pyrograms of the altered kerogens were much less complex than the unaltered samples, reflecting the thermal effects. The kerogens adjacent to the sills produce little or no pyrolysis products since these intrusions into unconsolidated, wet sediments resulted in in situ pyrolysis of the organic matter. Examination of the kerogens by ESR showed that spin density and line width pass through a maximum during the course of alteration but ESR g-values show no correlation with maturity. Stable carbon isotope (δ 13C) values of kerogens decrease by 1–1.5‰ near the sills at Sites 477 and 481 and the atomic N/C decreases slightly with proximity to a smaller sill at Site 478. Differences in maturation behavior between Site 477 and 481 and Site 478 are attributed to dissimilarities in thermal stress and to chemical and isotopic heterogeneity of Guaymas Basin protokerogen.

Meteorites and the Origin of Water and Reduced Carbon on the Earth

The meteorites called carbonaceous chondrites are believed to be unaltered material left over from the formation of the solar system. They contain substantial amounts of reduced carbon and of water in the form of hydroxyl ions. The oxidation state of iron in some carbonaceous chondrites has been determined by means of Mössbauer spectroscopy, and it is demonstrated that there is a correlation between the oxidation state of iron and the content of water and reduced carbon in the meteorites. Possible consequences of this fact for the origin of water and reduced carbon on the Earth are discussed.

Rock-Weathering Rates as Functions of Time

AbstractThe scarcity of documented numerical relations between rock weathering and time has led to a common assumption that rates of weathering are linear. This assumption has been strengthened by studies that have calculated long-term average rates. However, little theoretical or empirical evidence exists to support linear rates for most chemical-weathering processes, with the exception of congruent dissolution processes. The few previous studies of rock-weathering rates that contain quantitative documentation of the relation between chemical weathering and time suggest that the rates of most weathering processes decrease with time. Recent studies of weathering rinds on basaltic and andesitic stones in glacial deposits in the western United States also clearly demonstrate that rock-weathering processes slow with time. Some weathering processes appear to conform to exponential functions of time, such as the square-root time function for hydration of volcanic glass, which conforms to the theoretical predictions of diffusion kinetics. However, weathering of mineralogically heterogeneous rocks involves complex physical and chemical processes that generally can be expressed only empirically, commonly by way of logarithmic time functions. Incongruent dissolution and other weathering processes produce residues, which are commonly used as measures of weathering. These residues appear to slow movement of water to unaltered material and impede chemical transport away from it. If weathering residues impede weathering processes then rates of weathering and rates of residue production are inversely proportional to some function of the residue thickness. This results in simple mathematical analogs for weathering that imply nonlinear time functions. The rate of weathering becomes constant only when an equilibrium thickness of the residue is reached. Because weathering residues are relatively stable chemically, and because physical removal of residues below the ground surface is slight, many weathering features require considerable time to reach constant rates of change. For weathering rinds on volcanic stones in the western United States, this time is at least 0.5 my.

Effects of Basalt Intrusions on Kerogens in Unconsolidated Oceanic Sediments in Guaymas Basin, Gulf of California: ABSTRACT

Pleistocene sediments in Guaymas basin, Gulf of California, have been intruded by sills. Their organic matter was thus subjected to thermal stress. Samples from DSDP/IPOD Sites 477, 478, and 481 and from unaltered material from Sites 474 and 479 were analyzed to characterize the lipids and kerogens. The lipids of the thermally unaltered samples are derived primarily from algal and bacterial detritus. The samples near the sill contain the distillates; those closest to the sills contain essentially no lipids. The pyrograms of the kerogens from the unaltered samples reflect their predominantly autochthonous microbial origin. The pyrograms of the kerogens of the altered samples reflect the thermal effects by demonstrating a reduction in the complexity of the products, when compared with the unaltered samples. Kerogens adjacent to the sills produced little or no pyrolysis products. The effects of intrusions into unconsolidated sediments resulted in in-situ pyrolysis of the organic matter as confirmed by these data. End_of_Article - Last_Page 784------------

A note on low-grade contact metamorphism—southwestern Brewster County, Texas

SummaryIntrusion of the Bee Mountain soda microsyenite plug in southwestern Brewster County, Texas established conditions of low grade contact metamorphism in the upper Cretaceous Boquillas and Pen Formation sedimentary rocks. It is unlikely that load pressure exceeded 330 bars or that temperatures exceeded 470 °C at the intrusive contact. Thermally unaltered parent materials predominantly contain ortho- and allochemical low-magnesium calcite, silt-sized quartz, calcium montmorillonite, kaolinite, and volcanic glass. Incipient metamorphism is marked by the appearance of xanthophyllite followed by prehnite formed at the expense of xanthophyllite and montmorillonite. Near the soda microsyenite contact prehnite has decomposed to yield grossular and epidote group minerals, and apophyllite has replaced calcite where fluorine-bearing solutions have reacted with the parent material. Textural modifications include the recrystallization of calcite, redistribution of some of the mineral phases, and decreased friability in the marly layers.

Fine structure and distribution of extracellular polymer surrounding selected aerobic bacteria.

The structure and distribution of extracellular polymer surrounding Bacillus circulans, Diplococcus (Streptococcus) pneumoniae, Streptococcus salivarius, Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, Herella vaginacola (Acinetobacter calcoaceticus), and Agrobacterium tumefaciens were studied by electron microscopy. A modified ruthenium red staining procedure was used to examine the fine structure of capsule and slime. Freeze-etching and critical-point drying were used to examine the quantity of unaltered exocellular material. Comparative data demonstrate that fibrillar extracellular polymer surrounding B. circulans, D. pneumoniae, and K. pneumoniae is capsule (cell wall attached) which is characteristic of the producing organism. Capsular polymer generally appeared fibrillar, although globular polymer consisted of capsular subunits bound to S. salivarius and H. vaginacola. Exocellular slime was present about S. aureus, P. aeruginosa, and A. tumefaciens.

Properties of ‘Swelling’ Chlorite in Some Mesozoic Formations of California

AbstractSlaty strata and their weathering products comprise a large portion of the geologic formations of the western foothills in the Sierra Nevada, Mid-Northern California. The weathering products of Mesozoic slates in particular, locally known as ‘swelling’ chlorites, have caused numerous problems in road construction.A typical stratigraphic section of slates, which includes ‘swelling’ chlorites, is given for the area of Chili Bar, California, as part of the general geology of the western foothill formations. Remolded slate densities were observed to decrease while measured swelling pressures increased with increasing slate alteration. Swelling pressures in excess of 12.5 psi were observed. Curves are presented in comparison with DTA results showing the effect of alteration on the slate.The results of X-ray diffraction analyses, in correlation with i.r. data, show a typical slate mineral composition for unaltered material of about one-half chlorite with the remainder being about equal portions of muscovite and quartz. The entire chlorite content of the altered slate becomes a regular mixed-layer clay mineral, corrensite, which has been observed to alter to sedimentary vermiculite and Mg-saponite in residual soil. An i.r. absorption peak at 3690 cm-1 characterizes the mixed-layer clay mineral. Heat treatment of the mixed-layer clay mineral structure reduces the 14.3 Å basal spacing to 11.8Å at 540°C, which decreases to 10.6Å at 850°C, disappearing by 1050°C. Procedures are given for direct quantitative analysis of these three-phase mineral systems using simultaneous linear equations.Evidence is presented for the alteration minerals formed during weathering of the slate, including Fourier analysis of the mixed-layer clay structure.

On the Primordial Condensation and Accretion Environment and the Remanent Magnetization of Meteorites

Attention is drawn to the fact that neither astronomical observations, nor laboratory data can, as yet, sufficiently constrain models of the origin and evolution of the solar system. But, if correctly approached and interpreted, the magnetic remanence of meteorites could help in constructing a self-consistent model.In the context of various models for the early evolution of a solar nebula, the possible roles assigned to ambient magnetic fields and the paleointensities required to establish the stable natural remanent magnetization (NRM in range 10-4 to 10-1 cgsm) observed in meteorites, are discussed. It is suggested that the record of paleofields present during condensation, growth, and accumulation of grains is likely to have been preserved as chemical (CRM) or thermochemical (TCRM) remanence in unaltered meteoritic material. This interpretation of the meteoritic NRM is made plausible by experimental and theoretical results from the contiguous fields of rock magnetism, magnetic materials, interstellar grains, etc. Several arguments (such as the anisotropy of susceptibility in chondrites, suggesting alignment of elongated ferromagnetic grains, or the characteristic sizes and morphology of carrier phases of remanence, etc.) as well as general evidence from meteoritics (cooling rates, chemical and mineralogical data) can be used to challenge the interpretation of NRM as thermo-remanence (TRM) acquired on a “planetary” parent body during cooling of magnetic mineral phases through the Curie point in fields of 0.2 to 0.9 Oe.Fine-particle theories appear adequate for treating meteoritic remanence, if models based on corresponding types of permanent magnet materials, e.g., powder-ferrites for chondrites; diffusion hardened alloys for iron meteorites, are adopted, as suggested here.Finally, a potentially fruitful sequence of experiments is suggested for separating the useful component of NRM in determining the paleofield intensity and its time evolution.

Pitchfork Formation, Detrital Facies of Early Basic Breccia, Absaroka Range, Wyoming

The Pitchfork formation is here defined as the lowest series of beds in the southeastern part of the Absaroka Range, Wyoming. The Pitchfork formation consists largely of detrital rocks--sandstones, siltstones, and conglomerates--containing volcanic debris from eruptive centers in the Yellowstone Park-Absaroka volcanic province. The thickness of the Pitchfork formation ranges from about 200 to about 1,200 feet and is generally about 1,000 feet. The formation interfingers northward with the early basic breccia of Hague (1896 and 1899); toward the south it pinches out against the axis of the Owl Creek Range, forming the southern margin of the Bighorn basin. An estimated 80 per cent of the detrital beds are characterized by andesitic debris; dacitic detritus predominates in m st of the remainder. Most beds contain a small proportion of non-volcanic debris, and a few beds contain entirely non-volcanic material. Several varieties of tuff occur in this formation. Most of the detrital material was deposited in stream channels and floodplains, in a warm, humid climate. Both vertebrate and plant remains indicate that the Pitchfork formation is probably middle Eocene. The Pitchfork formation is almost everywhere underlain by the Willwood and Tatman formations of the Bighorn basin; it is overlain by the early basalt sheets of Hague (1896 and 1899) and equivalent breccia and by conglomerates of the late basic breccia of Hague (1896 and 1899). Several regional correlations of the Pitchfork formation and underlying beds are suggested. The Pitchfork formation intertongues with and is equivalent to the early basic breccia of Hague (1896 and 1899). Relationship of the Pitchfork formation to the early acid breccia of Yellowstone Park is uncertain; the early acid breccia may be older than the Pitchfork formation, but part of the early acid breccia may be equivalent to beds of the early basic breccia; hence, to part of the Pitchfork formation. Only traces of volcanic material are present in the Willwood and Tatman formations of the Bighorn basin, and much of this volcanic material is altered and is probably Paleocene or older. Unaltered dacitic material is locally abundant in the Wind River formation of the Wind River basin. Distr bution and lithologic character of the volcanic material in the Wind River formation suggest that it is a product of early Eocene eruptions probably representing the early acid breccia in the southern part of the Absaroka Range. The absence of similar volcanic material in equivalent beds of the Bighorn basin is explained by prevailing winds from the northwest or north. The Aycross formation, at the southern margin of the Absaroka Range, is probably correlative with the Pitchfork formation and the early basic breccia.

The Effect of Grinding on Micas

The general effect of grinding upon various minerals and the manner in which time of grinding affects cation-exchange capacity, etc., have been known for some time, but relatively little information is available upon the micas (Jackson and Truog, 1939; Kelley and Jenny, 1946; Parkert et al., 1950; Mackenzie and Milne, 1953). This, coupled with an observation made here on the pronounced effect of short-period grinding on muscovite, has led to a more detailed examination of the effects induced by such grinding upon some micas. Since the data for muscovite are completely discussed elsewhere (Mackenzie and Milne, 1953) only preliminary experiments upon biotite and vermiculite are recorded here. Materials and Methods . -The biotite employed occurred as segregations of small crystals in a nepheline-syenite pegmatite from Sutherland and is probably slightly impure*. The optical data were: = 1.584, #---1.626, y = 1.627, 2V small. The vermiculite, a very pure sample from Kenya, has been previously described (Walker and Milne, 1950). Each sample was divided into two parts, one of which was filed to pass 200-mesh, thus giving a powder of unaltered material, while the other was dry-ground in a mechanical agate mortar, samples being removed at various times up to 24 hours and sieved through 200-mesh. X-ray data were obtained with FeK ~ radiation and intensities were measured visually. Examination of some selected samples by differential thermal analysis was performed by standard methods using 0.20 g. samples (Mackenzie, 1952). A micro method was employed for determination of cation-exchange capacities (c.e.c.) (Mackenzie, 1951).

THE PROBLEM OF “WEANING” IN READING A FOREIGN LANGUAGE

Author's Summary.— An attempt to show when and how the shift from prepared, i.e., simplified, texts to unaltered material may be made.

The Effect of Leaching on Drift Pebbles

How different rocks endure the superficial agencies of leaching and solution may be seen from the composition of pebbles in bowlder clay where this has been subjected to the solvent action of meteoric waters. Many years ago the writer took occasion to collect fifty-eight lots of 1oo pebbles each, from bowlder clay in Louisa County, in Iowa. By collecting pebbles of one size, about one-half inch, and by taking all of this size to be found on a limited space of the clay surface, unconscious selection of different kinds of rock was avoided. Thirty-seven of these samples were taken from places where the drift was in its original condition, unchanged by subsequent weathering or decay. Twenty-one samples were taken from the upper part of the bowlder clay, where it had been more or less leached and weathered. In this region the bowlder clay is overlain by loess. The leaching of the clay sometimes extends five feet under the loess, but more often less than this. From this upper part of the till, calcareous material may be partly or entirely absent, so that there is no reaction for carbonates when acid is applied to the clay. Pebbles of limestone, which were no doubt originally present, have wholly or partly disappeared, and only less readily soluble materials remain. The leaching is most complete in the uppermost part of the till, and from here to the unaltered material below, is a zone in which the leaching is incomplete in varying degree. Limestone pebbles in this zone are either etched on the surface, or else they have suffered partial internal solution and are porous and even crumbling and are often yellow or brown from residual or infiltrated ferruginous material. Below is a table which gives the percentages of the most important rocks noted in the study of the pebble samples collected. In