OLD RED SANDSTONE, &c. , 37 



the earth appears to have remained in a state of repose for a long 

 time, which permitted new generations of organized beings to mul- 

 tiply on its surface, and mineral substances, carried by the waters, 

 to be deposited in great layers, and to entomb in their substance 

 the solid remains of the exuviae of contemporaneous animals and 

 plants. 



2. The first deposits which took place during this geological 

 opoch, constituted the strata of sandstone, conglomerate, (an assem- 

 olage of fragments of rocks and pebbles, cemented together by 

 other mineral matter,) clay, calcareous rocks, &c., and from theii 

 union resulted the formation called by geologists the old red sand- 

 stone, on account of its antiquity and prevailing colour. But this 

 state of things was soon changed, and there was formed, slowly 

 and gradually, at the bottom of the waters, an immense stratum of 

 calcareous rocks, seven or eight hundred feet in thickness ; then 

 the sandy sediment alternated with these limestones, and above this 

 great formation, designated under the name of carboniferous (coal- 

 bearing) limestone, numerous strata of sandstone, schistose clay 

 and coal were accumulated. 



3. The fossils of the old red stone are somewhat numerous, and 

 belong, for the most part, to marine animals, among which was a 

 fish of strange form, called Cephalaspis, (from the Greek, kephale, 

 head, and aspis, shield or buckler,) because its head resembles a 

 kind of buckler (fig. 29). 



Fig. 29. Cephalaspis Lyellii". 



The remains of the genus Cephalaspis (fip. 29) are found chiefly in the 

 apper beds of the old red sandstone of Scotland, but also in Herefordshire 

 And Wales. u In this genus, the head is very large in proportion to the 

 body, and occupies nearly one-third of the entire length of the animal; its 

 outline is rounded and crescent-shaped, and the lateral horns slightly incline 

 towards each other, their points being nearer to one another than they are 

 to the round part of the snout. The middle of the head is elevated, and 

 the sides dilated, so as to overlap the body, and extend considerably behind 

 it; but perhaps the head only appears to extend so far, owing to accidents 

 of displacement since the death of the animal. The eyes are placed in the 

 middle of the shield, near to each other, and are directed straight upwards. 

 It is imagined that the pointed horns of the crescent may have been useful 



1. What happened after the termination of the transition period of geo- 

 logical history ? 



2. What were the first deposits after the transition ppriod ? 



3. What is the character of the fossils of the old red sandstone ? What 

 is the Cephalaspis ? 



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