247 



Phyllodus and exhibited an unusual form. The palatine teeth 

 are composed of three or four central plates, surrounded by 

 others, as is represented in Agassiz's plates of the fossil fishes. 

 A perpendicular section shows them to be made up of several 

 layers, one above the other, sometimes five or six in number, 

 each layer being composed of dentine with a more compact 

 substance above it. 



Prof. Rogers said, that he considered the specimens exhibited 

 particularly interesting, as illustrating the relation of the Ameri- 

 can Tertiary to the deposits of the old world. The genus Phyl- 

 lodus occurs in the London clay. The eocene and miocene of 

 Europe are more closely related to each other than the layers of 

 Tertiary in America. The Richmond deposit is considered as 

 miocene. 



]\ir. Desor remarked that the London clay had been regarded 

 of late by some geologists as allied to the miocene. He agreed 

 with Prof. Rogers as to the want of a complete correspondence 

 between the American and European Tertiary, and also with 

 regard to the absence of a close connection between the Ameri- 

 can Tertiary of different epochs. 



Prof. Wyman exhibited a specimen of lignite from the Rich- 

 mon Tertiary. He stated that at the time it was dug up it was 

 quite moist and so soft that the fingers could be easily thrust 

 through it. After a few weeks exposure to the air it had dried 

 into a hard substance with a fracture like Cannel coal. 



Prof. Rogers said, that he had seen a similar hardening of 

 lignite after being taken from the earth. It often contains a 

 resinous matter which hardens in a short time. 



Dr. C. T. Jackson read a paper on a mineral named Jack- 

 sonile by Mr. J. D. Whitney. 



The purport of the paper was to show, that Jacksonite is not 

 a new mineral. This result was based upon examinations made 

 by himself and Mr. Crossley in his laboratory on pieces from the 

 specimen on which Mr. Whitney's examinations were made. 

 Mr. Whhney regarded it as an anhydrous mineral. Mr. 

 Crossley's examination detected 4.84 per cent, of water, — Dr. 

 Jackson's, 4.8 per cent. Adding this amount of water to Mr. 

 Whitney's formula, the result coincides with Walmsteadt's form- 

 ula for Prehnite, which mineral Dr. Jackson considered it to be. 



