108 



The following analysis of a variety of Slate, found in the 

 town of Somerville, Mass., near Boston, was commenced upon the 

 supposition that it was a Dolomite ; as the cleavage resembled, in 

 many respects, that of rhombohedral carbonates. 



The angle which the plane in the direction of the dip makes 

 with the plane of stratification is 102.*^ The angle which the 

 other plane of cleavage makes with that of stratification is 112'*. 



The angle which the two planes inclined to the plane of strati- 

 fication make with each other is llC, though this varies some- 

 what in different specimens. The specific gravity is the same as 

 that of Dolomite, being 2.8192. 



Analysis shows it to be a silicate of iron, alumina, lime, and 

 magnesia, in which the lime forms less than one per cent, of 

 the whole, as is shown by the following table : — 



Water 3.439 



Sesquioxide of Iron 8.324 



Sesquioxide of Alumina ,...*, 19.353 

 Lime ........ .625 



Magnesia 4.944 



Silica 63.238 



99.923 



The President exhibited the dilated vena cava of an 

 Otter, {Lutra Canadensis,) recently taken in Massachu- 

 setts, and explained the peculiar physiological condition 

 of this animal in connection with its diving habits. He 

 also pointed out some other interesting points in its 

 anatomy. 



Prof. H. D. Rogers made some remarks upon Ameri- 

 can and European Geology, in anticipation of a paper 

 which he said he intended to bring before the Society. 



Dr. T. M. Brewer read the following paper on Vireo- 



sylvia : — 



In the Proceedings of the Academy of Natural Sciences of 

 Philadelphia, (Vol. V. p. 153,) a description of a new species of 



