Murchison s Silurian System. 209 



strata of Devonshire, and to all the European coal fields; 

 Odontopteris obtusa, found also in Terrasson in France; 

 Pecopteris abbreviate*, also found near Bath in England and 

 Valenciennes in France, and two other species of the same, 

 P. lonchitica, Lind. Hutt. and P. blechnoides, Brong. com- 

 mon to all the European coal fields. Upwards of three 

 years after Mr. Murchison had communicated his views re- 

 garding the fresh water limestone of the Shrewsbury beds to 

 the Geological Society, certain carboniferous rocks were 

 described by Mr. W. C. Williamson, with notices of numer- 

 ous fossils which had been collected. From the silence of 

 Mr. Williamson regarding Mr. Murchison's observations in 

 Shropshire, it would appear he had been unacquainted with 

 them, and had therefore no suspicion that the calcareous 

 rocks he was describing bore any relation to this peculiar 

 coal measure limestone. Professor Phillips having visited 

 Manchester, he was furnished with a complete general sec- 

 tion of these beds, and at once detected the little micro- 

 scopic planorboid shell of the Shrewsbury rock, and follow- 

 ing up his inquiries he found other corresponding points; 

 and by these researches clearly proved that the limestone 

 and red marls of the coal formation at Ardwick near Manches- 

 ter were identical with the Shrewsbury beds described by 

 Mr. Murchison. 



" The upper carboniferous zone of Lancashire is thus identified by 

 mineral characters and by organic remains with the Shrewsbury coal 

 field, from which, however, it differs in exhibiting a much greater deve- 

 lopment of limestone, and with this increase of calcareous matter we 

 perceive a corresponding increase in number and variety of the remains 

 of animal life, particularly in the testaceous mollusca, whose existence 

 could not have been prolonged without an adequate supply of carbonate 

 of lime." Similar circumstances showing the increase of fossil shells 

 where calcareous rocks prevail, will be pointed out amidst the more 

 ancient strata. It is further interesting to observe in these rich fossil- 

 iferous beds of Manchester, the occurrence of a fish, Palceoniscus Freiesle- 

 beni, characteristic of the magnesian limestone ; another member of the 

 coal formation associated with some peculiar animal remains, and with 

 many plants and other fossils common to the ordinary coal measures ; 



