﻿lii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



ledge acquired of late years of the Silurian fauna reduces at once the 

 theory of successive development within very narrow limits ; for we 

 discover even in the lower Silurian, a full representation of the Radiata, 

 Mollusca, and Articulata proper to the sea ; and regarding it as a 

 marine fauna confined to those three classes, it might almost seem to 

 imply a more perfect development than that which peoples the ocean 

 of our own times. Thus in the great division of Radiata, we find 

 asteroid and helianthoid zoophytes, besides crinoid and cystidean echi- 

 noderms. In the Mollusca, M. Barrande enumerates, in Bohemia 

 alone, the astonishing number of 250 species of cephalopoda. In the 

 Articulata we have the crustaceans represented by more than 200 

 species of trilobites, not to mention other genera. 



The remains of fish, hitherto referred to lower Silurian rocks, have 

 proved on closer investigation to be spurious, those of the Wenlock 

 and Caradoc groups in England having been found to be portions of 

 zoophytes or crustaceans, or cystidean plates, and the ichthyolites, 

 supposed to be of like antiquity in the United States, being now 

 ascribed by some geologists to the upper Silurian, by others to the 

 Devonian era. Nevertheless, in the Bala limestone in Wales, an un- 

 doubted member of the lower Silurian, our Government Surveyors 

 have met with coprolites, which when analysed yielded between 30 

 and 40 per cent, of phosphate of lime, and bear witness to the exist- 

 ence of Vertebrata in the most ancient seas. Professor John Phillips', 

 in his memoir on the Malvern Hills and the palaeozoic districts of 

 Abberley and Woolhope, observes, that, on comparing the fossils of 

 the lower with the upper Silurian groups, he could discover no signs 

 whatever that the lapse of time had produced any improvement or 

 development in organic forms*. 



In the upper Silurian, we find, in addition to all the genera of the 

 invertebrate classes before enumerated, placoid fish, some of which 

 Agassiz refers to the cestraciont sharks, a family still existing in the 

 Australian seas, and which Prof. Owen places at the top of the highest 

 of eleven orders of fishes, ranged in an ascending scale of organi- 

 zation. 



The marine character of the Silurian rocks of Europe and North 

 America is sustained even in India by strata of the same age, as ap- 

 pears from the late investigations of Captain Strachey, who has ob- 

 * Mem. of Geol. Survey of Great Britain, 1848, vol. ii. p. 75. 



