300 



The first genus of the Brachiopodous Conchifera is Lingular 

 which is represented by the Lingula segis, from the roof 

 of the Middleton Coal ; but whether it extends to any other 

 seam I have not heard, though, from its marine nature, we 

 might expect it to occur in the Halifax CoaL The last 

 marine shell I have to enumerate is the Pecten Papyraceus^ 

 which I need scarcely say is the principal diagnostic fossil of 

 the Halifax Coal, and is found at its extreme limit in Derby- 

 shire. It occurs in great numbers, compressed into thin 

 layers, which rapidly decompose, from the quantity of iron 

 pyrites associated with them.* 



We now arrive at the extensive fresh-water deposit which 

 passes throughout the entire Yorkshire Coal Field, into 

 Nottinghamshire and Derbyshire. It is scarcely necessary 

 to say I allude to the seam or seams of iron-stone, filled with 

 such multitudes of fresh-water shells of the family Unionidse, 

 known as the mussel band. These shells were long supposed 

 to be of only two species, the Unio subconstrictus and 

 acutus. Capt. Brown, however, who has been investigating 

 these shells, has published a list of twelve more species from 

 the neighbourhood, under the genus Pachyodon, which are 

 as follow : — Pachyodon bipennis, Dawsoni, amygdala, 

 exoletus, antiquus, and pyramidatus, from Low Moor; 

 Pachyodon nanus, similis Blaydsii, transversus, and 

 levedensis, from Middleton; and Pachyodon turgidus, 

 from Wakefield. The appearance which these shells 

 present is worthy of notice, not only from the high state 

 of preservation in which they occur, (retaining in many 

 cases their original colour,) but from the circumstance of 

 their accumulation of all ages and sizes, living and dead; 

 some having been evidently dead before submersion, from 

 the fact of the valves being so widely extended, which is 



* In Lancashire, the Goniates and Pectens do not characterize a single bed, 

 but extend over Jive distinct beds. — Transactions of the Manchester Geological 

 Society, p. 88. 



