405 



Organic remains. — The fossils of the coal measures are described 

 with great detail, as well as the phenomena of beds containing marine 

 remains, alternating with others in which freshwater shells and land 

 plants occur ; and a comparison is made with the Canister coal-field, 

 in which similar alternations have been noticed. The following are 

 the principal points detailed in the paper respecting these alternations 

 at Coalbrook Dale. The lowest part of the coal measures presents nu- 

 merous beds of sandstone and shale, with seams of good coal ; some 

 of the beds containing in abundance vegetable remains, occasionally 

 associated with Unios. To these succeed the bed called the penny iron- 

 stone, in which has been found a few vegetable remains and casts of 

 Unios and Cyclades, but great abundance of marine remains belong- 

 ing to the genera Producta, Spirifer, Ammonites, Nautilus, Bellero- 

 phon, Conularia, Euomphalus, Pecten, Orbicula, Terebratula, Venus, 

 Asaphus, and Pentacrinites ; remains also of fishes, namely, the Megcd- 

 ichthys Hibbertii and Gyracanthusformosus. The next series of beds, 

 consisting of the usual alternation of sandstone, shale, and coal, in- 

 close vegetable remains and Unios. Upon these repose a stratum of 

 micaceous shale, containing ironstone nodules in which have been 

 found land plants, Unios in considerable quantities, remains of the Me- 

 galichthys and Gyracanthus, and Trilobites of a distinct genus. This 

 singular stratum is surmounted by a series, of great thickness, of the 

 usual coal measures, in which organic remains and land plants have 

 been observed, and is succeeded, in two localities, by the Chance 

 penny-stone, in which Produdus scabriculus occurs in vast abundance. 

 The uppermost beds of the series, consisting of many thick beds of 

 sandstone with layers of shale and one seam of coal, are almost de- 

 stitute of organic remains. The distribution of the fossils is extremely 

 irregular in different parts of the coal-field, being most persistent in 

 the lower beds ; and though they are most commonly found in the 

 ironstone nodules, yet they sometimes occur in the sandstones and 

 shales adjacent to the coal seams. 



In the concluding part the author reviews the facts detailed in the 

 memoir, and draws the inferences which he conceives they warrant. 



1st. Mr. Prestwich is of opinion that the alternations of freshwater 

 shells with marine remains, do not prove as many relative changes of 

 land and sea ; but that the coal measures were deposited in an estu- 

 ary, into which flowed a considerable river, subject to occasional 

 freshes ; and he conceives that this position is supported by the fact 

 of frequent alternations of coarse sandstones and conglomerates with 

 beds of clay or shale ; and for the same reason he is of opinion that 

 the vegetable remains did not grow where they are found. 



2ndly. After recapitulating the evidence in support of the protru- 

 sion of Coalbrook Dale through once continuous overlying forma- 

 tions, he calls attention to the important Inquiry whether there may 

 not be buried beneath the .new red sandstone districts other conside- 

 rable coal-fields, which are unknown, because they have not been sub- 

 ject to disturbing agents similar to those which exposed the district 

 under review. 



