Coal Series of Yorkshire. 353 



posits, zoological and minei alogical characters common to 

 both. Examined in detail, we find these characters not mixed, 

 but alternating in such a manner as if there had been one 

 periodical return of the marine element into its ancient re- 

 ceptacle, after that had been for some time occupied by fresh 

 water and its few inhabitants. The effects of this irruption 

 having, as it were, worn out, the zoological characters of fresh- 

 water deposits are again manifested at intervals in the muscle 

 bands, till the whole carboniferous system is entirely ended, 

 and marine exuvi;e reappear in the magnesian limestone. 



If, from whatever cause, we could witness the effects of a 

 general irruption of sea-water into a modern lake of great 

 extent and considerable depth, it is probable that the result- 

 ing phaenomena would be perfectly analogous in kind to those 

 described above. But this irruption of the ancient ocean into 

 the coal-basin of Yorkshire was probably not produced by 

 any violent convulsion i?i tliat basin, — for there is no uncon- 

 formity between the supposed marine and supposed fresh-water 

 deposits, — but by some disturbing causes originating at a di- 

 stance. As tlie elevation of the Western Alps has probably 

 occasioned the dispersion of boulders in Dauphine and Pro- 

 vence, and as the uplifting of the Scandinavian chain has been 

 followed by diluvial currents in Germany, without affecting 

 the position of the strata in those countries, so may the York- 

 shire coal district have felt the transient shock of some distant 

 convulsion. 



The periodical revolution in the nature of the waters which 

 operated the deposition of the lower coal strata in Yorkshire, 

 bears so remarkable an analogy to some of the phaenomena 

 of the marino-lacustrine tertiary deposits, that the same prin- 

 ciples will probably serve for a basis for the explanation of 

 both cases. In both instances we have a decidedly marine 

 deposit bcloW; and a decidedly lacustrine deposit above; the 

 intermediate ground is not exactly neutral, but sometimes 

 shows gradations from the one to the other, and sometimes 

 periodical alternations, — accompanied, however, by so entii'e 

 a parallelism of strata, that in seeking for the cause of these 

 changes, we are compelled to have recourse to agency at a 

 distance, — to the blocking up of the outlet of some estuary, 

 or to irruptions of the sea arising from subterranean distur- 

 bances in a difleient quarter. 



In a future communication to the Society, I sJiall describe 

 in detail all the species of animal remains which have been 

 obtxiined from this interesting part of the Yorkshire coal 

 strata. 



Third Series. \ ol. 1. No. .5. Nov. 1832. 2 Z 



