. Elements of geology : a text-book for colleges and for the general reader. Geology. TRANSITION FROM THE PALAEOZOIC TO THE MESOZOIC. 411 the Devonian, which is often called Old Eed sandstone. It is further distinguished throughout, especially the upper part, by variegated shales, and therefore called altogether Poikilitic group. It is also distin- guished throughout by the presence of salt, and therefore called the Saliferous group. Here, then, there were the strongest reasons for re- garding the whole as one group, distinctly separated by unconformity from the underlying Coal. The upper part
. Elements of geology : a text-book for colleges and for the general reader. Geology. TRANSITION FROM THE PALAEOZOIC TO THE MESOZOIC. 411 the Devonian, which is often called Old Eed sandstone. It is further distinguished throughout, especially the upper part, by variegated shales, and therefore called altogether Poikilitic group. It is also distin- guished throughout by the presence of salt, and therefore called the Saliferous group. Here, then, there were the strongest reasons for re- garding the whole as one group, distinctly separated by unconformity from the underlying Coal. The upper part of this continuous series contained undoubted Mesozoic fossils. The line of unconformity was, therefore, naturally believed to be the line between Palaeozoic and Meso- zoic. Unfortunately, the lower portion is very barren of fossils, and this means of correcting the stratigraphic conclusion was at first nearly wanting. When fossils were discovered in sufficient numbers, how- ever, they showed a greater alliance with the unconformable Coal below than with the conformable strata above. Thus, if we make the division between Palaeozoic and Mesozoic on stratigraphical grounds, we would find it between the Coal and the overlying strata; while, if we make it on paleontological grounds, we would have to draw the line through the midst of the conformable strata, a, giving one half to the Palaeozoic and the other half to the Mesozoic. The lower Palaeozoic half is called the Permian* As a broad general fact, therefore, the great commotion which is called the Appalachian revolution took place, or commenced to take place, at the end of the Coal period. But the fauna and flora were not immediately extermi- nated, but struggled on, maintaining, as it were, a painful existence un- der changed conditions, themselves meanwhile changing, until complete and permanent harmony was re-established with the opening of the Mes- ozoic. If we may use an illustration, the Appala- chian revolution was the
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectgeology, bookyear1892
