6 Silurian Fossils. 



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 Sur- 

 veyors have met with coprolites, which when analyzed yielded 

 between 30 and 40 per cent, of phosphate of lime, and bear 

 witness to the existence of Vertebrata in the most ancient 

 seas. Professor John Philips, in his memoir on the Malvern 

 Hills and the palaeozoic districts of Abberly and Woolhope, 

 observes, that, on comparing the fossils of the lower with 

 the upper Silurian groups, he could discover no signs what- 

 ever 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 organization. 



The marine character of the Silurian rocks of Europe and 

 North America is sustained even in India by strata of the 

 same age, as appears from the late investigations of Captain 

 Strachey, who has obtained from them a fine series of fossils 

 from the northern slope of the Himalaya mountains, more 

 than 200 miles north-west of Cashmere. Having therefore 

 as yet only discovered the deep-sea formations of this remote 

 period, we know nothing of the contemporaneous terrestrial 

 fauna. It is but lately indeed that our surveyors in Shrop- 

 shire have determined that land did exist at that period, and 

 have begun to trace out the boundaries of the shores of a 

 Silurian sea. 



In these most ancient of fossiliferous strata, I can neither 

 discern any signs of the dawn of organic life, or of an im- 

 mature and incipient condition of the animate creation, and 



* Mem. of Geol. Survey of Great Britain, 1848, vol. ii., p. 76. 



