bluuebunny/crossref_metadata_2025_split huggingface dataset:
Notes on some Analyses of Egyptian Igneous and Metamorphic Rocks
Authors: Hume W. F. , Harwood H. F. , Theobald L. S. , Awad A. I. 
Published: May 2009

1. The gneiss of the Sikait-Zabara district is in its mineral composition an aplitic granite, which has been subjected to intense pressure. It formed part of a magma of granitic composition which invaded a series of serpentines, themselves altered peridotites. The biotite-schist in many places immediately overlying the gneiss is the direct result of the assimilation of parts of the ultrabasic Tocks by the intrusive magma, the quartz, beryl, fluorite, tourmaline rock, and talc-schists associated with the biotite-schist bearing itness to the accompanying pneumatolytic action and silicification.2. The schist from Kosha in the North Sudan most nearlyresembles the acid gneiss of Wadi Shalul in the Eastern Desert of Egypt. If the latter were originally a granite, as has been suggested from the analysis, then the Kosha schist would itself be an intensely crushed granite containing potash and soda in approximately equal amount.3. The schist from opposite Khor Abdel Rahman in the North Sudan has been classified as fine-grained, epidote-albite-gneiss of uncertain origin.4. The schist between Khors Abu Dom and Sila in the North Sudan has been compared with the rock from the Lewisian formations of Coll in Scotland. It may be termed a hornblende-granulite,representing an extreme case of metamorphism with crystallization under great stresses of an originally sedimentary rock.5. The green schist from the Wadi Um Selman ravine, near the Dm Garaiat gold mine in South-East Egypt, is also regarded as an epidote-albite-gneiss, the bands being alternately quartzose and epidotic. The lime-containing minerals originally present have been altered to epidote and calcite.6. The rock from Da'aba Island, in the Second Cataract, is an oligoclase-mica-diorite-porphyry, the felspar having been proved to be more acid than originally concluded. This name has therefore to be adopted in place of labradorite-dolerite, the term applied to it in pi. lxxx of Hume's Geology of Egypt, ii, p. i, 1934.7. The rock of Arkasa Island, also from the Second Cataract, is, judging from the analysis, probably a more acid form of the oligoclase-mica-diorite-porphyrite series.8. The specimens Nos. 8 to 11 represent a group of rocks in which magnesite plays an interesting part in the composition.While No. 8 from Wadi Haimur is in the main a serpentine with but little magnesite, the remaining three rocks contain a notable percentage of this mineral. Pending further investigation, it is suggested that these changes may have taken place during periods when the ancient peridotites were submerged beneath the waters of the sea at various times in the geological history of Egypt.Dr. Hume desires to thank Mr. 0. H. Little, Director of the Geological Survey of Egypt, very warmly for having left Mr. A. I. Awad free to carry out the petrographical studies for this paper whenever circumstances allowed of his doing so. This paper is published with the approval of H.E. the Surveyor-General of Egypt.
On the Structure and Affinities of the Carboniferous CochliodontHelodus simplex
Authors: Moy-Thomas J. A. 
Published: May 2009

SUMMARY1. The anatomy ofHelodus simplexAg. is described.2. The skull is found to be holostylic, and to have many characters in common with the skull of the Holocephali, but in some respects is less specialized.3. The pectoral fins, with their long metapterygium, small propterygium, and fused anterior radials, resemble very closely those of the Holocephali.4. The pelvic and unpaired fins, and general body shape are found to resemble those of the Holocephali.5. It is concluded that the Cochliodonts are almost certainly closely related to the ancestors of the Holocephali, and the relatively unspecialized condition of the teeth gives support to the view that the holostylic condition of the jaws is primitive for the group. It is suggested that all the Bradyodonts were holostylic, that the hyomandibular may never have been suspensory, and that they may have diverged from the true Selachii before the hyomandibular played a part in the jaw suspension. The difficulties which this view involves are appreciated.6. The condition of the ethmoid region ofHelodussupports the view of the nature of the ethmoidal canal put forward by De Beer and Moy-Thomas (1935) rather than that of Allis (1917, 1926, 1934).
Symplectite-bearing Nodules in the Ardgour Marble, Argyllshire
Authors: Drever H. I. 
Published: May 2009

Summary and ConclusionsThe nodules examined have been shown to contain a variety of minerals and to exhibit certain mineralogical and structural differences from one another or within the nodules themselves. The mineralogical differences serve to separate five definite types of mineral facies. There are also described types transitional between the nodules themselves, and between them and the surrounding rock, grading from types sufficiently aluminous to exclude the formation of wollastonite to less aluminous types in which this mineral is formed.Owing to insufficiently prolonged variations of the metamorphic conditions equilibrium has not been established, and a remarkable series of replacement structures has been left in the rock by means of which the course of several stages of its metamorphism has been established.Lack of knowledge concerning the metamorphic conditions previous to changes due to the influence of the surrounding diorite, the isolated character of the nodules and the intricacy of the relationships between the minerals render the origin and metamorphism of these nodules subject to a variety of interpretations. The balance of evidence seems in favour of the one put forward here.
A Mid-Carboniferous Boulder-bed near Settle
Authors: Dixon E. E. L. , Hudson R. G. S. 
Published: May 2009

(1) The blocks of limestone in the Bowland Shales of School Share include a variety of rock-types of northern (Yoredale) facies and come from several beds near the Orionastraea Band of the Upper Viséan.(2) They are a local accumulation at the local base of the Namurian (Upper Bowland Shales; zone of Eutnorphoceras pseudobilingue, E1 and rest, with evidence of some slight erosion, on one of the highest horizons of the Viséan (Lower Bowland Shales; zone of Goniatites spiralis, P2). Their horizon, therefore, is that of the mid-Carboniferous unconformity of Settle and elsewhere.(3) They mark a comparatively small faunal hiatus (between the newsomi-meslerianum level immediately below and the C. malhamense level above).(4) Their separation from the parent rocks and their assemblage are not due to tectonic causes. On the other hand, their great size points to some unusual form of transport.(5) As they occur in a shale series near the Craven Faults they may legitimately be explained as the result of land-slips down s muddy slope from a limestone cliff, probably a fault-scarp raised by the mid-Carboniferous earth-movement.(6) The circumstances recall those attending the Lower Palaeozoic conglomerates of Quebec. A recent explanation ascribes these to landslips caused by earthquakes from submarine fault-scarps. The School Share landslip may well have been caused by earthquakes, and the scarp from which the blocks were derived may have been essentially submarine.
The Contact Metamorphism and Related Phenomena in the Neighbourhood of Marulan, New South Wales
Authors: Osborne G. D. 
Published: May 2009

1. The contact metamorphic effects produced by the intrusion of quartz-monzonite into the Silurian limestone of the Marulan district, New South Wales, are described.2. The rocks are divided broadly into marbles, hornfelses, skarns, and hybrid diopside-rocks. The first two groups are interpreted as being due to the recrystallization of limestone containing impurities which have reacted with the lime of the sediments to give lime-silicates and certain other minerals. The view is taken that only a very minor amount of pneumatolytic metamorphism followed the main thermal change. The skarns are shown to be due to the metasomatic replacement of recrystallized limestone by magmatic solutions rich in iron and silica, which were also responsible for the deposition of iron-oxides in cracks.The hybrid rocks are explained as developing from limited marginal assimilation of limestone by the quartz-monzonite magma.
The Geology of Skerryvore, Dubh Artach, and Sule Skerry
Authors: Walker Frederick 
Published: May 2009

Skerryvore consists of acid gneiss with dark bands containing biotite and hypersthene. The mica was probably formed by the recrystallization of chloritic matter by heat from an underlying plutonic mass. The islet is cut by a 2 foot north-south dyke of olivine-dolerite.Dubh Artach forms part of a sill of ophitic olivine-dolerite and is probably of Tertiary age.Sule Skerry consists of andesine-anorthosite into which dark streaks consisting of hornblende and quartz have been injected at a later date to form a banded gneiss.
The Geology of Jebel Usdum, Dead Sea
Authors: Wyllie B. K. N. 
Published: May 2009

SummaryThe salt of Jebel Usdum is not a product of the Pleistocene Dead Sea, nor of the lake which preceded it (in ? Pliocene time), the waters of which were fresh for a long period and deposited sediments, with a maximum thickness of 1,000 feet or more, which are younger than the salt.
Batholiths of Southern Rhodesia
Authors: Macgregor A. M. 
Published: May 2009

THE problem of the formation of the larger masses of granite is receiving considerable attention by geologists at the present time, and it is hoped that the following observations and surmises regarding the granites of Southern Rhodesia may be of more than local interest. Southern Rhodesia forms part of a typical Pre-Cambrian shield and consists, apart from younger formations, of about 74,000 square miles of granite and gneiss intrusive into 13,000 square miles of older rocks. The area has undergone tremendous denudation, which took place mainly during the Pre-Cambrian, and the structures exposed, therefore, are different from those seen in regions where only the peaks of granite masses have been uncovered.At the outset I wish to thank Mr. H. B. Maufe for permission to draw from the store of information, much of it unpublished, which he has collected in the Geological Survey Office at Salisbury, and also for having the accompanying illustrations drawn in the office. This information includes both petrological and structural data, but it is only the structural aspect of the problem which it is intended to discuss here.
The Genesis of Oligoclase in Certain Schists
Authors: Turner F. J. 
Published: May 2009

The mineralogical changes in green schists and related quartzofelspathic schists of sedimentary origin are discussed, and the following conclusions are reached as to the conditions of formation of oligoclase in these rocks:—(1) Oligoclase normally appears as a product of dynamothermal metamorphism at relatively high grades such as prevail in the zones of almandine and perhaps kyanite. It is accompanied either by deeply-coloured hornblende, hornblende and biotite, or biotite and muscovite, according to the chemical composition of the rocks in which it occurs.(2) Sodic oligoclase containing 10 per cent to 15 per cent of anorthite may occur with pale aluminous hornblende in green schists lying within the more strongly metamorphosed portion of the chlorite zone. The rocks in question are low in potash and have been formed by reconstitution, at a higher grade, of chlorite-epidotealbite-schists containing calcite. This oligoclase-hornblende association is not to be confused with the actinolite-epidote-albite-chlorite assemblage which is formed at any grade within the zone of chlorite, by direct reconstitution of basic igneous rocks without change in bulk composition and in the absence of CO2. A slight modification of Tilley’s subdivision of the green schist facies of Eskola is therefore introduced.(3) A zone of oligoclase representing a grade of metamorphism higher than that attained in the biotite zone, may be recognized for quartzo-felspathic schists of appropriate composition and for many green schists, in areas of progressive regional metamorphism. In the latter case, blue-green hornblende often accompanied by biotite is also present.(4) Oligoclase or more calcic plagioclase and deeply-coloured hornblende form readily during purely thermal metamorphism of only medium grade in the absence of stress. This accounts for the irregular distribution of both these minerals in districts where purely thermal and regional metamorphism have both occurred during the same period of orogeny.
On the Structures of the Dermal Ethmoid Shield of Osteolepis
Authors: Westoll T. Stanley 
Published: May 2009

SUMMARYThe structure of the fronto-ethmoid shield ofOsteolepis macrolepidotusAg. is described fully for the first time, and the homology of the dermal bones is discussed. The most interesting feature is the recognition of the existence of a sensory-canal bone bearing teeth in the position of the premaxillary of Tetrapods, with which it is shown to be homologous; the nomenclature of the equivalent bones suggested by Säve-Söderbergh is discussed and revised.The presence of a continuous cosmine sheet overlying several bones is emphasized, and the problem of growth of such a combination is brought out. It is shown that the problem can be solved by extensive resorption and redeposition of cosmine, and this hitherto unnoticed change is demonstrated in a number ofOsteolepids and in some Dipnoi. The results of the resorption are to free the bones of the head from the cosmine, and thus to expose the top of the true bone ; the new characters are those usually associated with different genera, usually placed in distinct families.Finally it is noted that the resorption involves a general chemical change affecting cosmine all over the body, which it is suggested may be due to the release of an internal secretion, the whole process of resorption and redeposition of cosmine being cyclic and almost certainly seasonal, growth being therefore a seasonal change.
On the Mechanics of Mountains
Authors: Jeffreys Harold 
Published: May 2009

SummaryIt appears that the geophysical approach to the problems of crustal dynamics leads to a theory of mountain formation that covers the main features of the formation of nappes and is in general agreement with other geological evidence. The chief novelty is in the recognition of the importance of the spreading under their own weight of the rocks uplifted as a result of crustal shortening.
The Genetic Relationships of Pegmatites, Aplites, and Tin Veins
Authors: Derry D. R. 
Published: May 2009

SUMMARYFrom the conclusions regarding the formation of complex pegmatites from the field and microscopic evidence, the following sequence of events is suggested:—Towards the end of the solidification of a granite magma a liquid remains, having the general composition of a common pegmatite, but with small quantities of sodium and some rarer elements. By squeezing during crystallization this magma is separated into two distinct parts, one of which forms common aplite dykes. The other, more aqueous portion, when tapped by fissures, solidifies more slowly to form dykes, sills, or stringers of common pegmatite. During this solidification the albite (in solution), together with rare elements and their compounds, is concentrated in the remaining liquid portion, which now contains a very high proportion of water. This aqueous solution begins to migrate up the dykes or sills of common pegmatite, possibly even before the latter has completely solidified, showing a preference for the foot-wall, and begins to replace the earlier minerals, The first stage is the replacement of potash felspar, either microcline or orthoclase, by albite. Later there is a replacement of albite and sometimes of earlier minerals by spodumene, lepidolite, cassiterite, tantalite, etc. Cassiterite, possibly due to being carried in combination with a volatile element tends to be deposited in the uppermost part of the dyke or sill, where, however, some albite replacement has always preceded it.
Notes on the Geology of Sula Sgeir and the Flannan Islands
Authors: Stewart Malcolm 
Published: May 2009

SummarySula Sgeir consists of hornblende-gneiss with occasional biotite and augite. The whole is intersected by small pegmatite veins which merge along the borders into the gneiss. Though evidence is small, it seems probable that the island, together with North Rona, came under the influences of the Quaternary ice.The Flannan Islands consist also of hornblende gneiss, biotite being a fairly common accessory. Numerous and varied pegmatite Veins occur throughout the islands, and in certain cases have affected the foliation of the gneiss. Owing to the proximity of the islands to the Lewis and the Harris, and the presence of adeposit of cemented sand on Eilean Ghobha, it seems probable that the Quaternary ice also reached these islands.
Dolerites Associated with the Karroo System, South Africa
Authors: Daly Reginald A. , Barth Tom F. W. 
Published: May 2009

Summary—The field impression of a high degree of uniformity in the composition of the intrusive Karroo dolerites over a vast area is confirmed by new chemical and microscopical studies. The pyroxene characteristic of the dolerites is a typical pigeonite, which, however, does not display any twinning on (100). The plagioclase is potash-free, usually a labradorite, but it has been observed that a homogeneous crystal of plagioclase may be in twin position to another homogeneous crystal of a very differently composed plagioclase. The close resemblance of the doleritic liquid to the artificial liquid taken by Bowen to represent basaltic liquid is noted, and his conclusion that pyroxene and feldspar should crystallize simultaneously in natural basaltic liquid is confirmed.Conceivably the doleritic liquid was quite original and not a differentiate of any earlier liquid. However, analogies like those with the tholeiites and similar hypabyssal rocks of Great Britain suggest that in South Africa, as in Great Britain, the liquids of these hypabyssal rocks were derived from the slightly more femic plateau-basalt.On that assumption the question of the mode of differentiation arises. The fractional crystallization of plateau-basalt, as now described by Bowen and other leaders, does not appear competent to explain the abnormally low soda of one of the analyzed dolerites, nor the excess of soda and total alkalies in plateau-basalt respectively over the soda and total alkalies of the Karroo dolerite. Further, the settling-out of early olivine does not explain the excess of (total) FeO in plateau-basalt over the (total) FeO in the Karroo dolerite. The actual relations indicate the need of renewed examination of the theory of magmatic differentiation by crystal-fractionation. In any case many more data are required before it is possible to decide upon the precise relation of the Karroo dolerite to a parental magma. Possibly such additions to knowledge may annul present difficulties in the way of accounting for the composition of the dolerite.
The Petrography of the Hunstanton Red Rock
Authors: Rastall R. H. 
Published: May 2009

At Hunstanton Cliff and at Snettisham there is a gradual transition, without physical break, between the Carstone and the Red Rock. At Hunstanton there is a physical break, marked by a solution-surface, between the Red Rock and the Sponge Bed. At Snettisham the Red Rock is incomplete at the top.The Carstone shows a peculiar and characteristic assemblage of mineral constituents, with much glauconite and ferruginous ooliths. The heavy minerals are notable for the abundance of kyanite and staurolite and rarity of garnet.The Red Rock consists of three fractions: (a) calcium carbonate, (b) red mud, (c) sand. This sand is exactly like the Carstone, with the same heavy minerals, and it continues, though in diminishing amount, up to the very top of the Red Rock.The insoluble residue of the Sponge Bed is entirely different: it consists mainly of silicified foraminifera, with a few colourless quartz grains, and it contains no heavy minerals at all.There is an abrupt and complete lithological change at the base of the Sponge Bed.The red fraction of the Red Rock is rich in Fe2O3, and Al2O3, and it is suggested that it is of lateritic origin.The precise manner of formation of the Red Rock is not explained. It has not been found possible to visualize a set of conditions under which fairly large pebbles, ferruginous sand grains, ferruginous ooliths, red mud, and calcium carbonate were all deposited at the same time.It is suggested that the red mud is due to lateritic material derived from a neighbouring land area.The heavy mineral assemblage shows that the material of Carstone type did not come from the north, and probably not from the west. The only possible source is the Caledonian and Armorican plateau of London-Brabant or a continuation of it under the North Sea. The sudden change at the top of the Red Rock is due to the submergence of this land area by the Cenomanian transgression, which in Norfolk was accompanied by local erosion: this finally closed the source of supply of the heavy minerals: here and there a slight recurrence of transport of lateritic material gave rise to pink bands in the Chalk at higher horizons.The interpretation by Messrs. Kitchin and Pringle, on palaeontological grounds, of the relations of the Red Rock to the Carstone and to the Chalk is shown to be quite inconsistent with the results of this petrographical investigation.
On an Inverted Mass of Upper Cretaceous Strata near Leighton Buzzard, Bedfordshire; and on an Overlap of the Upper Gault in that Neighbourhood
Authors: Kitchin F. L. , Pringle J. 
Published: May 2009

Summary of Conclusions.We may summarize our chief conclusions as follows:—(1) The brachiopod-bed of Shenley Hill, as described by Messrs. Lamplugh & Walker, who referred it to the Lower Greensand, is shown by stratigraphical and palæontological evidence to be of a composite character. Its constituent parts belong respectively to the basement-bed of the Upper Gault and to the basement-bed of the Cenomanian stage, as understood by English geologists (sub-zone of Catopygus columbarius).(2) The Cenomanian bed is present in the form of isolated lenticles of limestone. Although no comparable stratum can be found at the present outcrop, which has receded from the area where conditions produced this particular type of deposit, the bed has a close lithological counterpart in Northern France (Matringhem), where there is an almost identical bed at the base of the varians zone.(3) At Harris's Pit the Cenomanian bed, an inconstant layer of Upper Greensand formerly seen above it, and an overlying mass of Gault Clay of rostratus age are in an inverted order of succession. There is a junction of erosion and non-sequence between the Gault and the Cenomanian bed.
Some Unmapped Faults in the Lower Carboniferous of Westmorland and their Relation to the Dent Fault System
Authors: Miller A. A. 
Published: May 2009

Summary and Conclusions1. The Dent Fault diminishes in throw towards the north, and is almost non-existent 3 miles south of Kirkby Stephen.2. The principal line of dislocation is then displaced about a mile to the east, where there is a steep monoclinal fold, replaced sometimes by a fault, running in a direction parallel to the Dent Fault and also having a downthrow to the east.3. Further parallel faults, many of them hitherto unmapped, assist in the subsidence of the country to the east.4. Cross-faults, in most cases with downthrow to the south, accommodate the margin of the “Rigid Block” to local increase or decrease of throw.5. These two systems of faults are of approximately the same age, and were brought about by the same crustal movements.