38 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [ June 3, 



also found in the S.E. of Ireland, in strata which by their place in 

 the series, and by other associated fossils, are also considered to be 

 true Lower Silurian. 



Now, whilst the Cystidea occur in thick clusters in the north of 

 Europe, where peculiar calcareous conditions abound, they are com- 

 paratively rare in our schistose, muddy deposits of the same age. So 

 is it with the genus Illcsnus, of which /. crassicauda is the type, which 

 swarms in the Lower Silurian of the Baltic provinces of Russia, but 

 which is not so abundant in Scandinavia where the conditions change, 

 and which only occurs as a rare fossil in British rocks of the same 

 age. 



If indeed the presence of a few peculiar fossils in certain tracts 

 were to be admitted as the test of the individuality or isolation of 

 the stratum in which they occur, then truly may many new names 

 be proposed for the protozoic group. On this principle, the lower 

 black schist and limestone of Scandinavia, containing some organic 

 remains specifically unknown in England, might be termed the 

 Odinian group, in honour of the mythic deity of the early in- 

 habitants ; whilst in the new continent, the strata which (as Mr. Lyell 

 believes) occupy the same horizon, might from their geological 

 outcrop be named Canadian. But these local appellations, whether 

 Petropolitan, Odinian or Canadian, are, after all, nothing but the 

 already typified Lower Silurian strata, which in several regions 

 have been seen to repose on masses in which no signs of animal life 

 have been discovered. 



For the above reasons, and others cited in my previous works, 

 particularly in the first chapter on Russia, I am of opinion that 

 Professor Sedgwick's recent proposal to establish a Cambrian group*, 

 as distinguished from the Lower Silurian, cannot be sustained, and 

 that the attempt to introduce such a group, as founded on observations 

 in tracts often replete with igneous rocks both contemporaneous and 

 posterior, and which has been subjected to so many dislocations, will, 

 if intended for general use, necessarily lead to much confusion, par- 

 ticularly among foreign geologists. Such a question must, I appre- 

 hend, be definitively settled by appealing to countries like Scandina- 

 via,Russia and America, where the very rocks in question are spread 

 over enormous horizontal areas, or in slightly inclined and undisturbed 

 positions, without the trace of contemporaneolis disturbances of the 

 sea in which their remains were entombed, and where the strata, the 

 lowest in position which contain organic remains, can be actually 

 seen to repose on pre-existing mineral masses void of such remains. 



It is not by finding, after several years of elaborate research, a 

 few undescribed and rare British palaeozoic forms, that the age of 

 rocks can be determined. The true tests are order of superposition 

 and the common or prevalent fossil types ; for if amid forms pecu- 

 liar to one or two localities, the prevailing typical shells of a previously 

 named group should occur in lower or thicker strata ; or if the 

 band in question can be followed into other tracts where the usual 

 types abound, the point is determined. 



Objecting therefore entirely to this proposal, because I now know 

 * See Quart. Geol. Joum. Vol. ii. p. 130. 



