410 



PALEOZOIC SYSTEM OF ROCKS. 



on the Carboniferous ; and, corresponding with this unconformity, 

 there is a wonderful change in fauna and flora — a change the greatness 

 of which we have attempted to show in the contrast on the preceding 

 page. Now, the older geologists regarded this change as one of instan- 

 taneous destruction and recreation, because they took no account of a 

 lost interval. But we have already shown (pp. 181, 295) that in all 

 cases of unconformity there is such a lost interval, which in some cases 

 is very large. In order to account for the very great change in the 

 organic world, it is only necessary to suppose that periods represented 

 by general unconformity are critical periods in the earth's history — 

 periods of rapid change in physical geography, climate, and therefore 

 of rapid change in fauna and flora, by the passing out of old types and 

 the differentiation of new types. Unfortunately, in the earth's history 

 as in human history, it is exactly these critical periods — these periods of 

 change and revolution — the record of which is apt to be lost. In both 

 histories, too, this is truer the farther back we go. Of the long inter- 

 val between the Archaean and Palaeozoic, not a leaf of record has yet 

 been recovered with any certainty ; but of the interval now under dis- 

 cussion many leaves of record have been recovered. These have been 

 bound together in a separate volume or chapter and called the Permian. 

 I shall regard the Permian, therefore, as essentially a transition period ; 

 its rocks were deposited during the period of commotion ; its fossil 

 types are in a state of change, though more nearly allied to the Palae- 

 ozoic. 



From what has just been said, it will be anticipated that the uncon- 

 formity of the Mesozoic on the Palaeozoic sometimes takes place be- 

 tween the lowest Mesozoic and the Permian, and sometimes between 

 the Permian and the Coal. The Permian, therefore, is sometimes con- 

 formable with the Coal, as, e. g., in this country , sometimes conform- 

 able with the Triassic, as in England. It thus allies itself stratigraphi- 

 cally sometimes with the Palaeozoic, sometimes with the Mesozoic. 

 Paleontologically it is always more allied to the Palaeozoic. The Eng- 

 lish section, and the history of opinion concerning it, admirably illus- 

 trate this point. Fig. 587 is an ideal section through the Devonian, 



the Coal and Tri- 

 assic (Lower Meso- 

 zoic) of England. 

 Lying unconforma- 

 bly on the eroded 

 surface of the Coal, 

 £, there is seen a continuous and perfectly conformable series of strata, 

 a. This series, moreover, is lithologically characterized throughout, 

 especially the lower part, by frequent alternations of Eed sandstones, 

 and therefore has been called New Red sandstone, to distinguish it from 



Fig. 587. -(After Lyell.) 



