72 



THE SILURIAN PERIOD. 



CHAP. 



If we arrange these strata in five groups, and mark in each the 

 occurrence of remains of the classes of marine animals, we shall 

 have the following Table : 



No. 



1 s I 

 II II 



= iv. 



SI -in. 



Here it appears very plainly that a complete system of invertebral 

 marine life, with all the principal divisions now in existence, was 

 fully established in the middle of the Silurian period, as it is known 

 at Malvern ; also that this system had come in gradually from a 

 small beginning, and died out almost completely with the Ludlow 

 rocks, the strata above being comparatively poor in life. Fishes 

 appear only in the later deposits; no reptiles, no birds, no mam- 

 malia. 



The series of lower palaeozoic rocks in the Malvern region is 

 perhaps the fullest known in so small a tract. It is not indeed 

 quite complete. The succession of lower palseozoic rocks in Wales 

 and the bordering counties may be represented in the following 

 Table ; the black shale and Holly bush sandstone of Malvern prob- 

 ably corresponding to the Tremadoc or upper Ffestiniog rocks : 



