PALJEONTOLOGICAL REPORT OP. GEOLOGICAL SURVEY. 545 



torn is a micaceous coarse fire-clay, full of SUgmaria, resembling sand- 

 stone shales. This is all that we can possibly say of this bed, which 

 entirely disappears, at least as an isolated bed, in all the part of the 

 coal-fields that we have explored. The shaft of the Henderson Com- 

 pany shows there its total absence; at the Hollo way boring its place 

 only is marked by a three feet two inches bed of black shales, with 

 some little coal ; at the Airdrie shaft there is no trace ol it; at Curlew 

 and Mulford's, coals No. 9 and No. 11 are open on the same hills, and 

 the place of No. 10 is indicated only by a coal dirt. If we had found 

 it at any other place the remarkable conformation of its fire-clay would 

 have afforded an easy identification of it. The only way of account- 

 ing for its disappearance is by supposing that it is generally part of 

 coal No. 11, and tbat at Shawneetown Company mine, where it is separa- 

 ted from it by forty-three feet of shales, it has somewhat gone out of its 

 way. Perhaps this is the cause of the irregular and sometimes large 

 thickness of No. 11, and of its one and sometimes two clay partings, 

 also very variable in their thickness. 



There is about the position of this bed a difference between the to- 

 pographical assertions and our own. But this difference is probably 

 caused by mistaking, in some places, No. 11 for No. 10. With such 

 beds, unreliable in their directions, the topography, by itself, and 

 without the aid of. the palaeontology, must necessarily lead to error. 



Coal No. 11. This is a peculiar, generally very fine and well de- 

 veloped bed of coal, though varying from two to nine feet in thickness. 

 We have previously observed, that as regards the remains of fishes, espe- 

 cially, there is a remarkable identity in the palseontological characters 

 of this and No. 9 coal. The shells appear to be generally of different 

 species, and especially distributed in a different proportion. From the 

 notes of Mr. Cox, who may perhaps change the nomenclature of the 

 shells after a more careful examinatiou, No. 11 coal is especially characr 

 terized by an abundance of Pleurotamaria of various species; Pror 

 ductus Eogeri? (N. and P.;) Nucula Hameri? and by a large Avicula f 

 resembling Avicula rectalateraria, but larger and with a difference in 

 the ribs of the side wings. The fossil plants are not so generally dis- 

 tributed in those shales as in No. 9, especially the Sigillaria seems to 

 be wanting. The shales also are of finer texture, more bituminous, 



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