CAMBRIDGE ESSAYS : HOPKTXs' ^'gEOLOGy/^ 427* 



has been, and is still, departing from some primitive state Widel3r dif- 

 ferent from its actual one, and approaching to some ultimate condition 

 to which it can only attain, under the action of recognized physical 

 causes, after an indefinite period of time, though its approximation to 

 that ultimate condition not only is now, but has been for an enormous 

 period of time, so near as to admit of no change the rate of -^hich can 

 be deemed perceptible." 



In the early stages of a science, the observed phenomena are littld 

 more than so many insulated facts, but with accumulated observations 

 there arises a necessity for classification. The phenomena thus 

 classified are suggestive of hypotheses as to the physical causes to which, 

 the phenomena are due, and hence the science becomes inductive. 



The subject is, then, thus divided : — 



1. Descriptive Geology. — The description of the observed pheno- 

 mena of inorganic matter, and this arrangement into groups exhibiting 

 the laws by which they may be connected. 



2. PALiEONTOLOGT. — The braucli which treats of the phenomena of 

 organic matter, and of the stratigraphical and geographical distribution 

 of fossil organic remains. 



3. Physical Geology, which comprises all those investigations and 

 discussions by which we endeavour to connect the phenomena with the 

 physical causes to which they arc due. 



In accordance with this plan, Mr. Hopkins now proceeds to state the 

 broad generalizations of this science and the conclusions immediately 

 deducible from them, restricting himself to those points, whether facts 

 or theories, which are regarded as firmly and finally established ; and 

 afterwards discussing some questions of high speculative interest, on 

 which there still remains room for differences of opinion. The first fact 

 to which attention is directed is " the division of the superficial portion 

 of the earth's crust into two distinct portions, stratified and un- 

 stratified. 



"The unstratified portion of the earth's crust is distinguished by the 

 total absence of all stratification. In some cases there are planes of 

 separation, termed divisional or structural x^lanes, which might, at first 

 sight, deceive an inexperienced eye, but which are soon seen to be 

 totally distinct from planes of stratif.cation. Its calcareous, siliceous, 

 and argillaceous constituents exist much more in mineralogical combi- 

 nation, the first being in much smaller proportion, and the general 

 structure is far more crystalline than in the stratified mass. Granite 

 may be instanced as one familiar form of unstratified rock. 



''But there is a far more important and significant distinction be- 

 tween these stratified and unstratified masses. The former contains 

 within it, imbedded in almost every stratum, the remains of organic 

 objects, animals and plants ; whereas no trace of such objects is found 

 in the unstratified mass. They comprise great numbers of bones of 

 vertebrate, and shells of invertebrate animals, with numerous remains 

 of zoophytes. The great majority of these remains are completely 

 mineralized, every particle of animal or vegetable matter having entirely 

 disappeared, and been replaced by mineral substances. It is beautiful 



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