1879.] -»«" [Genth. 



piece. It is impossible to say that it is a fossil, nor could a fossil, unless 

 previously silicified, be preserved in a rock so highly metamorphosed. 



"I do not believe it to have been a pebble. The extremely elongate form 

 and elliptical section would in my opinion preclude that view of the matter. 



" Should you ever obtain specimens of which you could spare a thin slice, 

 it would be the best method of determining the nature of the material. 



Fig. 4. 



" The enclosed material lies apparently in the plane of the bedding or lam- 

 ination of the enclosing rock. The substance is too thin to give an idea of 

 the full original form, but from its outline I infer that it has been similar 

 to the other specimen" (Fig. 5). " The outline is, in my opinion, quite too 

 symmetrical for a pebble, and, while we have no evidence of its organic 

 character, it is not easy to give any satisfactory explanation of its origin. 



"The specimens are extremely interesting and others should be sought 

 for. J. Hali,." 



Since the receipt of the above letters the other specimens have been 

 sent to the writer by Dr. Stubbs. 



On Pyrophyllite from Schuylkill County, Pennsylvania. By F. A. Genth. 

 (Bead before the American Philosophical Society, July 18, 1879.) 



One of the most interesting varieties of pyrophyllite is that from the 

 coal slates of the " North Mahanoy Colliery " (old Silliman Colliery) near 

 Mahanoy City, Schuylkill county, Pa. 



It had been mistaken for damourite, until, by chemical analysis, I estab- 

 lished its true character. 



I am indebted to Mr. Eli S. Reinhold, of Mahanoy City, for specimens 

 and for the following information with reference to its occurrence. 



In the bed, known as " Buck Mountain," it is usually found in hori- 

 zontal seams, parallel with the coal beds, although it occurs at times in 

 irregular seams in other directions. Thus far it has not been found in any 

 of the other beds of the same mine, and only this mine has furnished It, 

 although the bed in which it occurs is worked in other mines. It also is 

 observed as marking or constituting the plant impressions on the coal slates 

 at this locality. 



It is found in thin seams of a delicate fibrous structure. At first glance 

 much resembling the serpentine-variety "chrysotile." It seems that this 

 pyrophyllite has been filling up cavities and cracks in the coal slate, and 

 the exceedingly delicate impressions left by the coal plants in the slate are, 

 after their decay, filled up with pyrophyllite material. Then, it is often 

 not thicker than the finest tissue paper, but still shows, when magnified, 

 the fibrous appearance. In larger cracks it seems to have crystallized from 

 above and from below, and the two seams, thus formed, are mostly sepa- 

 rated by a thin layer of pyrite in minute crystalline masses, which leave 

 the impressions of their crystals upon the pyrophyllite. Frequently the 

 fibrous pyrophyllite, as well as the pyrite, are coated with a very thin 

 layer, not thicker than the finest tissue paper, of a scaly variety of pyro- 



