Theoretical Considerations. 



439 



result from any modification of stilbite or Heulandite. There is, 

 therefore, as much reason for making- this mineral a distinct species, 

 as there was for separating Heulandite from stilbite. I am aware 

 that mineralogists have of late exceedingly multiplied species by divis- 

 ions of the stilbite of Hauy. Beudant, especially, in the last edition 

 of his mineralogy, (1830,) has made no less than five: viz, stilbite, 

 Heulandite, epistilbite, hypostilbite, and spherostilbite ; the two last 

 being added by himself. He supposes that when the same elements 

 combine in different and definite proportions and under different 

 forms, they should constitute different species ; although in external 

 characters they differ but slightly ; and surely no scientific man can ob- 

 ject to this principle. But recent discoveries have shown that the same 

 elements, combined in the same proportions, are capable of crystalizing 

 in forms incompatible with each other. This may prove to be the 

 case with some of the new species separated from stilbite, and with 

 Lincolnite among the rest. Yet at present it seems as well entitled to a 

 distinct name as Heulandite, and better than hypostilbite and spheros- 

 tilbite, whose crystalline form has not been ascertained: much better 

 also than epistilbite, since the controversy concerning it that has been 

 carried on in the European Journals. When this subject shall be 

 better understood than it now is, mineralogists may find it necessary 

 to reform the list of species ; nor can we now say which of them 

 must be striken out. 



Theoretical Considerations. 



There has been so decided a change within a few years in the 

 opinions of geologists as to the origin of the trap rocks, and there is 

 now so general an agreement in regarding them as igneous products 

 of early times, that a prolonged discussion of the subject in this place 

 will not be necessary. I shall only state the leading arguments in 

 support of this opinion, that will apply to the greenstone of Massa- 

 chusetts. 



1. The resemblance in external characters between some varieties 

 of our greenstone and the products of existing volcanoes. The 

 amygdaloids are the most striking in their resemblance. In the val- 

 ''ey of the Connecticut it is easy to collect a suit of specimens of this 

 description, that could hardly be distinguished from specimens that 

 are frequently brought from the craters of volcanoes, except by the 

 greater freshness of the latter. Let a man pass from Bridgman's 

 tavern in the southeast part of Amherst to Granby, over the east part 



