We also wish to recognize Stephen Langer, Ph.D., psychologist in Olympia, WA, and Robert L. Maxwell, Jr., for contributing to the clinical and computer analyses.Reprint requests should be addressed to Lloyd I. Cripe, Ph.D.,
The Microscopic Structure of the Charnwood Rocks. In many cases the task of determining the nature and structure of these rocks is comparatively easy; but in others it presents great difficulties. These arise from the amount of metamorphism which the rocks have undergone since they were first deposited. This metamorphism may be said to be of a double nature :—the one, readily apprehended by the eye, that which has converted sandstone into quartzite, and fine felspathic detritus into something resembling a felspathic igneous rock, being in all probability the combined effect of pressure, heat, and water; the other, almost wholly revealed by the microscope, in which the last of the above-named agents of change has probably been the most active, and which may still be in progress—namely, the gradual decomposition of the minerals which once composed the rocks, and the formation of new ones by fresh combinations of the chemical elements thus set free. This process often obscures, far more than the former, the original structure of the rock; and it is this accordingly which causes our main difficulty in the study of these Charnwood rocks. To investigate microscopically all the varieties of stratified rocks found in the Forest would be a most laborious task; and in all probability the result would not compensate for the labour. We have therefore selected a series of specimens which appeared either typical of the more important varieties, or likely to be useful in illustrating some point of structure or stratigraphy. Forty-four slides in
The huge masses of chalk in the glacial drift on both sides of Cromer, and especially at the headland near Trimingham, have for many years attracted the attention of geologists. In this Magazine (Dec. II, Vol. VII, 1880, p. 55) and in the Survey Memoir on the Geology of the Country around Cromer, published in 1882, Mr. Clement Reid ascribes those at the latter place to the advance of an ice-sheet by which the chalk has been thrust up into a kind of fold and the flint layers have been bent, illustrating his interpretation by a diagrammatic section. We visited the Cromer cliffs for the first time in 1892, and after a careful examination of the Trimingham headland, not only felt more strongly than before certain weak points in Mr. Reid's reasoning, but also observed some facts difficult to reconcile with his conclusions. Since that date we have more than once visited these sections, and found last April that comparatively recent inroads of the sea had made great changes which had shown the relations of the chalk and glacial drift to be, in our opinion, incompatible with Mr. Reid's interpretation.
A t the opening of this paper I desire to acknowledge my great obligations to Professor Bonney for his assistance throughout my investigations. I must also thank J. R. Cousins, Esq., of St. John’s College, Cambridge, for valuable help. Little has hitherto been written on the geology of Guernsey which would be of much use to a visitor. Macculloch contributed a brief account to one of the earliest publications of this Society. Ansted’s book on the Channel Islands contains some remarks on its general features. There are two papers by Professor Liveing, with which in many respects I cannot agree, in the Cambr. Phil. Soc. Proc. vols. iii. and iv., and one by Mr. J. A. Birds in the Geol. Mag. for 1878, which contains some accurate observations. A few interesting but short papers on raised beaches and the like complete the literature of the subject. How scanty is the information furnished thereby may be imagined from the fact that not one of these publications contains a geological map; and the sketch map (Pl. XX.) which accompanies this paper is, so far as I know, the first which has ever been published. Any map shows clearly enough the triangular shape of Guernsey, and with a glance at the scale of miles its dimensions can be easily estimated. But most maps do not even attempt to indicate the remarkable physical difference between the northern and southern parts. A spectator on the deck of a steamer approaching St. Peter’s Port sees on the
Much study has been bestowed, upon the boulders included in the Glacial Clays, their nature, origin, and distribution. The matrix in which they lie has received comparatively little attention. Yet the matrix, in many or most, forms by far the largest part. I have been endeavouring to study this matrix under the microscope, by washing it, shaking it up with water, and so separating the material which will settle quickly to the bottom from that which remains longer in suspension. The process has to be repeated until the water remains clear, else dust still suspended dries on the surfaces of the grains which had settled and masks them from examination. I have collected and dried this finer dust, but it cakes together: I have not obtained from it much information. The coarser material, that which subsides first, forming from 40 to 75 per cent. of the whole, dries to a sand or powder and lends itself readily to examination with the microscope. I have tried several methods, and have succeeded best by inspection under direct daylight of the powder strewn on a slide. Inspected in this manner, Glacial Clays from localities in East Anglia tell something of their sources. I have examined specimens from places along a belt of country in Suffolk extending from Lowestoft to Bury St. Edmunds, a distance of more than 50 miles; Lincolnshire material dredged up in deepening the ship-channel to Boston (kindly sent by Mr. W. H. Wheeler, C.E.); Cambridgeshire specimens from Ely Cemetery and
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