100 



as its quantity is not constant, he did not consider it an essential 

 ingredient. 



Dr. Gould asked, if pressure had caused the appearances in 

 question, how could this explanation be admitted, in the case of 

 the markings on the Venus ? The specimen was from the Nan- 

 tucket bluff, remarkable for the undisturbed and unopened condi- 

 tion, and perfectness of its shells. If the markings were caused 

 by sea-weeds, he thought the red color might be explained without 

 ascribing it to Manganese. All the deep water sea-weeds, and 

 animals, such as Crabs and Star-fishes, are red when first drawn 

 up, but turn green in a short time. 



Mr. Teschemacher replied that he had been unable to ascertain 

 whether the particular shell exhibiting the markings in question, 

 had been subjected to pressure or not. As to the change of 

 color referred to by Dr. Gould, he remarked that the mineral 

 Chameleon, which changes its color so curiously under the 

 influence of light, is an oxide of Manganese. 



Mr. J. D. Whitney said he did not consider pressure necessary 

 to explain these phenomena. The dendritic is a well known 

 form of crystallization. On the shell exhibited, it followed the 

 line of a crack, as is often seen in chemical experiments. 



Dr. Bacon stated that he had seen such forms on Quartz crys- 

 tals, where there was no crack to guide them. It was evident, 

 therefore, that such an arborescence might be independent of any 

 leading line. 



Mr. J. D. Whitney read the following remarks on the 

 composition of Chloritoid or Chlorite-spar, and Masonite. 



" The true chemical composition of the substance called 

 chloritoid is a matter of some uncertainty. BonsdorfT, who, 

 according to G. B-ose, undoubtedly analyzed the real chloritoid, 

 in which water was an essential ingredient, gave as the result of 

 his analysis, 



■^^' ' Si + A12 Si + 3H; 



j. 



- Mg3 

 the ratio of the oxygen of R, Al, Si and H, being 



