34 



SEA PLANTS, CORALS, ETC. 



granite The sub-groups of this system are it. the follow- 

 ing succession upwards: — L, hornblende slate ; 2, chiasto- 

 lite slate ; 3, clay slate ; 4, Snowdon rocks (grawacke 

 and conglomerates) ; 5, Bala limestone ; 6, Plynlymmon 

 rocks, (grawacke and grawacke slates, with beds of* con- 

 glomerates.) This system is largely developed in the 

 west and north of England, and it has been well examined, 

 partly because some of the slate beds are extensively 

 quarried for domestic purposes. If we overlook the dubi- 

 ous statements respecting Sutherland and Bohemia, we 

 have in this " system" the first appearances of life upon 

 our planet. The animal remains are chiefly confined to 

 the slate beds, those named from Bala, in Wales, being 

 the most prolific. Zoophyta, polyparia, crinoidea, con- 

 chifera, and Crustacea * are the orders of the animal king- 

 dom thus found in the earliest of earth's sepulchres. The 

 orders are distinguished without difficulty, from the ge- 

 neral characters of the creatures whose remains are found ; 

 but it is only in this general character that they bear a ge- 

 neral resemblance to any creatures now existing. When we 

 come to consider specific characters, we see that a diffe- 

 rence exists — that, in short, the species and even genera 

 are no longer represented upon earth. More than this it 

 will be found that the earliest species comparatively soon 

 gave place to others, and that they are not represented 

 even in the next higher group of rocks. One important 

 remark has been made, that a comparatively small variety 

 of species is found in the older rocks, although of some 

 particular ones the remains are very abundant ; as, for 

 instance, of a species of asaphus, which is found between 

 the laminae of some of the slate rocks of Wales, and the 

 corresponding rocks of Normandy and Germany, in enor- 

 mous quantities. 



Ascending to the next group of rocks, we find th<* 

 traces of life become more abundant, the number of species 

 extended, and important additions made in certain ves- 

 tiges of fuci, or sea plants, and of fishes. This group of 

 rocks has been called by English geologists, the Silurian 



* In the Cumbrian limestone occur " calamopora, lithodendra, 

 cyathophylla, and orbicula." — Philips. The asaphus and trinucleus 

 (crustacep) have been found respectively in the slate rocks ot 

 Wales, and the limestone beds of the grawacke group in Bohemia 

 That fragments of crinoidea, though of no determinate species oc 

 cur in this system, we have the" authority of Mr. Murchison.— 

 Silurian System, p. 710 



