99 



January 3, 1849. 

 The President, in the Chair. 



Present, twenty-nine members. 



Mr. Teschemacher called the attention of the Society to 

 the fact, that some years since, he had exhibited, at one of 

 its meetings, specimens of a curious slaty substance found 

 in digging a well in Newton, on which were beautiful den- 

 dritic forms. At that time his impression, and that of Mr. 

 G. B. Emerson was, that these markings were the remains 

 of sea-weed, and were produced by external pressure. 

 Analysis showed them to be composed of Manganese. Mr. 

 Teschemacher, at that time, tried the experiment of pres- 

 sing clay between layers of glass, and succeeded in pro- 

 ducing similar appearances. 



He now had to exhibit to the Society a Venus^ from the Nan- 

 tucket oyster bank, which bore on its inner surface, precisely 

 similar dendritic markings, of a reddish color, following the line 

 of a crack. He was inclined to consider these markings also as 

 due to sea- weed, subjected to pressure. Their chemical charac- 

 ter was the same as that of the specimens formerly exhibited. 

 He was unable as yet, to say whether Manganese is a constituent 

 of sea-weed, or not. The lines are somewhat finer than the 

 fibres of the sea-weed, but this he thought might be explained 

 by supposing Manganese to be present in very small quantity, 

 while the other constituents of the sea-weed had disappeared. 

 The color was also to him an evidence of the origin of these 

 markings. 



Mr. Teschemacher also stated that these forms had been found 

 on the new mineral, Idocrase^ found by Prof. Webster, in Maine. 

 As this is an eruptive mineral, of course it can contain no sea- 

 weed. In this case he supposed liquid Manganese had been 

 subjected to pressure. Manganese is an element in Idocrase^ but 



