436 



Scientific Geology. 



two miles northeasterly from Bloody Brook meeting house, were 

 quite large. The largest of these specimens, nine by six inches in di- 

 ameter and weighing 23 pounds, was composed of an outer zone of 

 greenish chalcedony half an inch thick : then a zone of flesh colored 

 chalcedony: the center consisted of an amethystine geode. The 

 best of these specimens which I have been able to procure for the col- 

 lection (No. 1191,) is about six inches by four : the outer zone is car- 

 nelian : the second bluish chalcedony, and the remainder limpid 

 quartz, almost filling the cavity. When the outer coat is broken off, 

 the specimen shows a strong resemblance to the human skull ; exhib- 

 iting protuberances and depressions enough to satisfy the most sanguine 

 phrenologist. Another specimen, three inches in diameter, exhibited 

 no less than 14 concentric bands, consisting of chalcedony and quartz 

 of various colors. This is a genuine fortification agate. Sometimes 

 fortification and eyed agates are exhibited in the same specimen. It 

 is to be feared, however, that this locality is nearly exhausted ; at least, 

 until a long period of time shall have decomposed the greenstone 

 much deeper. 



Calcareous spar is one of the most frequent of the minerals in the 

 greenstone of Massachusetts ; both in that in the eastern part of the 

 State and in the Connecticut valley. Generally it is the laminated 

 variety ; sometimes flesh colored, but mostly limpid. Often it consti- 

 tutes the cement of trap tuff Sometimes it is in distinct crystals. 



A few years since Prof. Silliman detected selenite in amygdaloid 

 from Deerfield. It was white and retained its water of crystalization. 



Several species of the zeolitic minerals have been found in this rock, 

 in the Connecticut valley. Analcime has been frequently said to be 

 quite common; but I am suspicious that calcareous spar has been 

 confounded with that mineral ; and I dare not say that it exists in our 

 greenstone. Nor am I sure that laumonite occurs as far north as 

 Massachusetts, although the greenstone in the vicinity of New Haven 

 contains it. As to chabasie there is no doubt but it has been found in 

 Deerfield, one mile east of the village. It is always crystalized, and 

 almost invaribly in the primary form, an obtuse rhomboid. The crys- 

 tals vary from l-50th to l-4th of an inch on their sides; and these 

 are grouped on tabular and pseudomorphous quartz, on prehnite, and 

 on the greenstone : either in fissures, or more commonly in the cavi- 

 ties of the amygdaloid. This mineral seems to have entered these 

 for the most part at a later period than many of the others with which 

 it is associated. For often we find it in the upper part of a cavity 



