EASTERN MASSACHUSETTS. 



403 



exist in the vicinity under the " deep alluvion " on account of the " largo 

 patches and fragments" which he found there {I. c, p. 1G8), In his 

 section Dr. Eaton represents hornblende rock as extending from Frani- 

 ingham to Boston, and dipping towards the sea at a gentle angle. Un- 

 derlying this blanket of hornblende rock was gneiss, and then granite. 

 Most of his information regarding the geology of Boston seems to have 

 been taken from the Messrs. Dana's Outlines, referred to in the preced- 

 ing pages, 



iVecording to the Eev. Elias Cornelius, the rocks at the eastern por- 

 tion of the peninsula on which the city of ,Salera was built *' are either 

 a pure granite, or that variety of it called sicnite, the hornblende of 

 which is diffused in diiferent proportions, from a few specks scarcely 

 discernible, to very considerable quantities/' (Amer. Jour. Sci., 1821, 



(I) in., I). 232.) 



Dr. Thomas Cooper later remarked that " no person accustomed to 

 volcanic specimens can look at the porphyries from the neighborhood of 

 Boston, in my possession, and doubt of their volcanic origin." (Ibid., 



1822, (1) IV., p. 239.) 



In bis Sketch of the Geology, &c. of the Connecticut, Trof. Edward 

 Hitchcock states that epidotic and syenitic greenstones belonging to the 

 Transition exist in the vichdty of Boston, and that dikes of basaltiform 

 greenstone occur in the syenitic granite in the same region, (Ibid., 



1824, (1) VIL, p. 30.) 



In a section given l)y Dr. Amos Eaton in his " Geological and Agri- 

 cultural Survey of the District adjoining the Erie Canal," beginning at 

 Boston and pas^sing through Waltham, Weston, Sudbury, and Framing- 

 ham, the country-rock is represented as being *' hornblende rock includ- 

 ing all its varieties." This rock is given as extenduig from Boston to 

 midway between Framingham and Shrewsbury, and is iigured as having a 

 steep easterly dip. A patch of argillitc is represented as horizontally 

 underlying Harvard College and resting on the upturned edges of the 

 '' hornblende rock," 



lu tlio description of a section made by Prof. Edward Hitchcock, and 

 placed a,t the end of the above-quoted work, the rocks in the vicinity of 

 Boston are said to be syenite, argillite passing into greenstone slate, 

 pudding-stone, amygdaloid, transition argillite, greenstone, and petrosili- 

 ceous porphyry. Veins of dark compact greenstone are said not to be 

 uncommon in syenite and syenitic granite, in the vicinity of Boston. 

 He cites Dr. J. W, Webster as authority for the statement *' that the 

 only rock ever found in situ in Boston" is syenite. A peculiarity of 



