On the constitution and history of grits and sandstones / by J. Arthur Phillips.

  • Phillips, J. Arthur (John Arthur), 1822-1887.
Date:
[1881]
Catalogue details

Licence: Public Domain Mark

Credit: On the constitution and history of grits and sandstones / by J. Arthur Phillips. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    On the Constitution and History of Grits and Sandstones. By J. Arthur Phillips, Esq., F.G.S. [Plates I. & II.] The careful and exhaustive researches relative to the constitution and mode of formation of arenaceous rocks which have recently been published by Professor Daubree, Dr. Sorby, and others, leave open a comparatively restricted field for the pursuit of similar investiga- tions. Having, however, during the last two years paid considerable attention to the study of rocks of this class, I now venture to bring before the notice of the Geological Society some facts and deductions therefrom which would appear to have escaped the attention of previous observers. For the convenience of developing certain ideas relative to this subject, I propose in the present paper, in the first place, to describe various grits and sandstones which have been microscopically and otherwise examined. In doing this the older rocks will be con- sidered first, and those of more recent age subsequently noticed in the order of their geological sequence. The chemical composition of some typical rocks will also be given. Secondly, the results of observations bearing on the efiPects pro- duced by the action of flowing water on particles of sand and gravel transported thereby will be described ; and finallj', the more impor- tant observed facts will be summarized, and their bearings discussed. The difierence between grit and sandstone is one not always distinctly marked ; and numerous definitions of the two rocks, often somewhat contradictory, have been given by various geologists at different times. It has even been stated by an eminent authority that rocks which in the north of England would be called grits, receive the name of sandstones in the south*. In order, therefore, to avoid misunderstanding upon this point, I may state that in the following descriptions the term grit is applied only to coarse-grained arenaceous rocks of which the com- ponent fragments are for the most part angular, and which, although frequently crystalline in structure, seldom contain either perfect or nearly perfect crystals. The cementing material of such rocks is, as a rule, highly siliceous. Sandstones differ from grits in being finer in structure than the latter, and in their component grains being usually less completely incorporated with the cementing medium. The quartz in many sandstones occurs principally in the form of perfect crystals, or in that of crystalline aggregations. In quartzites the spaces between the component grains are com- pletely filled by a siliceous cement, in wliich respect they closely resemble some varieties of fine-grained grit. * ‘Mauual of Geology,’ by John Phillips, F.R.S., p. 654.