Ranges of Sieniti 



455 



augitic granite ; although in position it is associated with granite. 

 There are two varieties. The first is composed of black hornblende, 

 greenish augite, and yellowish feldspar ; all the ingredients except 

 the feldspar exhibiting a very distinct and lively crystalline structure. 

 This variety occurs in the northern part of Belchertown. The other 

 variety, which I have found only in bowlders in Amherst, consists of 

 augite and feldspar ; the former being so arranged in the latter as to 

 present the appearance of letters. (Nos. 1362, 1363.) 



Topography of Sienite. 



The eastern, and northeastern parts of Massachusetts most abound in 

 sienite. A large part of Essex County is based upon it, as are several 

 towns in Middlesex. On the south of Boston it spreads over a large 

 part of Norfolk county and some part of Plymouth. A glance at the 

 map will show where it prevails most extensively. In all these places 

 it forms hills of moderate elevation with no very striking characters. 

 Its particular situation in respect to greenstone and granite I have 

 already described in treating of the former rock. 



The only other place in the State where I have met with sienite in 

 place, is in the valley of the Connecticut. Here I have marked two 

 deposits of considerable extent. The first extends from Mount Hol- 

 yoke in Belchertown to Chickopee river and a little beyond: the oth- 

 er, on the west side of the Connecticut, occupies a considerable part of 

 Northampton and Hatfield, and extends to the center of Whately. 



Although sienite very much resembling that which exists in the 

 valley of the Connecticut occurs in the eastern part of the state, yet 

 none like that which is so commonly employed for architectural pur- 

 poses in the eastern part of the state, known as the Gluincy and Cape 

 Ann sienite, is found in the valley of the Connecticut. Nor have 

 I met with any in that valley which is porphyritic. Indeed, I have 

 arranged all which has come under my observation in that valley, 

 under the quaternary compound described as the third variety in giv- 

 ing the mineralogical characters : although I doubt not but one or 

 more of the four ingredients may sometimes be wanting. Perhaps 

 all of this sienite might properly be described as sienitic granite, or 

 granite which takes a proportion of hornblende into its composition. 



The sienite in the Connecticut valley occupies a low level, rarely 

 rising into hills of more than 100 or 200 feet high: And on the west 

 side of the river a considerable part of the formation is buried up by 

 diluvium and tertiary strata. 



