462 Scientific Geology. 



of Northampton and Whately, have been mentioned. Associated 

 with these, I have sometimes found a mineral crystalized in four 

 sided prisms, which I have been disposed to refer to red oxide of tita- 

 nium. The best place for obtaining these minerals, particularly the 

 quartz, is in Whately, about two and a half miles south of the meet- 

 ing-house. Some of the drusy surfaces of this quartz present a curi- 

 ous pseudomorphous appearance. (No. 1369,) It is precisely such 

 an appearance as would result from making random cuts in the 

 quartz, while in the state of a paste, with a thin bladed knife. Obvi- 

 ously it has proceeded from the infiltration of the quartz around some 

 mineral in thin plates, originally occupying the cavities and subse- 

 quently decomposing. 



Following the eastern margin of this sienite about a mile south in- 

 to Hatfield, from the locality last mentioned, we find a vein of sulphate 

 of baryta, from one to four feet wide, running by the magnetic needle 

 W. 22 1-2 N. and dipping about 90. This baryta is the gangue of 

 sulphuret of lead, blende, and pyritous copper. It has been excavated 

 several feet and the quantity of baryta thrown out is immense. 



Theoretical Considerations. 



Sienite is very rarely found in Massachusetts in continuous veins in 

 other rocks like granite and greenstone. Sometimes, however, as I 

 have formely stated, it penetrates sienite of a different variety, or 

 greenstone, in so many directions and in such large quantity, that the 

 rock so penetrated is divided into numerous fragments forming a kind 

 of breccia. Even in these cases, the sienite which thus forms veins, 

 contains but little hornblende. Upon the whole the argument in fa- 

 vor of the igneous origin of sienite from the mechanical or chemical 

 effects of its veins, is comparatively feeble. 



In the conglomerated sienite which has been described, however, I 

 think we have a peculiar and forcible argument in favor of the form- 

 er fusion of this rock by heat. Some other theoretical inferences 

 also result from the facts in this case, which will need more minute de- 

 tails than have yet been given. 



I have frequently observed this variety of sienite in the eastern part 

 of the state. But there the nodules are so much changed in their 

 characters that they seem to be only a variety of sienite. It is in the 

 valley of the Connecticut that the most interesting and striking facts 

 on this subject are developed ; and in that valley Whately is the place 

 that most particularly claims attention. The following imperfect 



