366 Proceedings of the British Association. 



the limestone (E) under the coal, was shown the state of the sea 

 of that period. There were the Productas, (the P. antiquata 

 group,) the Lithostrations, and the Syphonophyllia, resembling 

 those of the English and Irish carboniferous limestone, and the 

 Pentremites sufficiently characteristic to afford a good temporary 

 designation for the deposit. One fossil would seem to have 

 strayed from its proper place, (the Calceola,) but as no single 

 shell could be regarded as marking the boundary of a formation, 

 this was not an exception to the law ; the evidence given by a 

 large number of forms proved these beds to be the equivalents of 

 our carboniferous limestone. Beneath this limestone occurred a 

 fine sandstone (D) ; the identity of its fossils was doubtful ; it 

 were unsafe to call them Silurian ; the Spirifer represented was 

 evidently one of that peculiar Producta-like group with trans- 

 verse bars, belonging to the carboniferous limestone, and the 

 other fossils seemed to indicate an intermediate term of life. In 

 the lower limestone (B) a Pleurorhynchus was found, — a genus 

 which occurred in Devonian, but not in the Silurian rocks; Pen- 

 tremites were also figured as belonging to this deposit. The low- 

 est deposits (A) forming the basis of the series, contained the 

 usual Silurian forms, Orthidas and Spirifera. These rocks ap- 

 peared as one series of calcareous deposits, formed under circum- 

 stances less subject to fluctuation than their equivalents in Eu- 

 rope ; and the continuity of specific forms and types of organiza- 

 tion seemed to have been much greater than in countries where 

 physical changes produced well-defined lines of separation in the 

 deposits. The successive periods of deposition of strata were 

 much better determined by organic forms than by the mineral 

 constitution of the rocks, but in applying this principle it is im- 

 possible to be too cautious, the evidence being not of time but of 

 circumstance; the character of the organic remains being deter- 

 mined by the physical conditions of the period. The order of 

 physical changes, and the series of organic life, must be inquired 

 into separately, and their results combined before we could be 

 safe : he had no intention of interfering with or undervaluing in- 

 vestigations based on other grounds, but he believed he had pre- 

 sented a view which did not clash in its result with that given 

 by investigations of another kind. 



Mr. Sedgwick contended, that the expression law was not used 

 in a correct sense, if by using it, we excluded the idea of laws of 



