CHAPTEE VIII. 



THE POIKILITIC PERIOD. 

 PEEMIAN, TKJASSIC, AND EH^ETIC DEPOSITS. 



WE now enter on a very different series of rocks, accumulated 

 under new conditions, on the eastern side of the great palaeozoic 

 region of Malvern and Wales. For this series the term Poikilitic 

 has been at different times employed by myself; but of late years, 

 not on account of mineral distinctions, or of different physical 

 origin, the lower portion has been separated under the title of 

 Permian, imposed by Sir R. Murchison on a great development 

 of it which he explored in Russia. Some time previously I had 

 proposed the separation, on the ground of the fossil contents , of the 

 magnesian limestone series of England from the new red series, 

 to which by mineral affinities and physical origin it is naturally 

 allied, and had united it with the carboniferous system, to con- 

 stitute an upper palaeozoic period. Both of these views have been 

 adopted the Permian system as denned by Murchison a , and the 

 relation of its fauna to that of the carboniferous system as an- 

 nounced by myself b . 



In some respects and in some districts it is, however, more con- 

 venient to adhere to the old established alliance of the Permian 

 many-coloured deposits, with the variegated sandstones and clays 

 of the new red series ; for the physical history of these two great 

 groups is on the whole one great sequence of natural operations. 

 There are indeed cases, as in Lancashire and Cheshire, and in 

 a less degree in Derbyshire, where a kind of gradation appears 

 between the coal formation and the Permian sandstones which are 



a Memoirs on the Geology of Russia, by Sir R. I. Murchison, M. de Verneuil, and 

 Count Keyserling, in Geol. Soc. Proceedings, 1842, 1843, &c. 



b Penny Cyclopaedia, article ' Sal iferous System ;' also Palaeozoic Fossils of Devon 

 and Cornwall, 1841, p. 160. Conybeare employed the term Pcecilitic. 



