1878.] 313 [Wadsworth. 



Rock port granite, standing side by side with the Quincy syenite of 

 Gore Hall. 



In attempting to account for this diversity of statement, very many 

 of the buildings in Boston constructed of the Rockport stone, were 

 examined: and several thin sections were made (at the time when 

 those of the Quincy syenite were prepared) of Rockport stone that 

 could be procured from the stone yards in this vicinity. All the 

 sections were of granite, and to the best of my recollection, all the 

 buildings examined were of the same material, except part of the 

 the west side of the Beacon Hill reservoir, where it is partially 

 hornblendic, and the Boston Post Office. 



Last autumn I was able to visit Rockport twice, for several hours 

 each time. My examinations show that both the syenite and granite 

 exist in Rockport and Gloucester; but the latter is the rock princi- 

 pally quarried. The places examined were the cuttings along the 

 railroad from Gloucester to Rockport, and from Rockport northward 

 beyond Pigeon Cove. I am indebted to Mr. J. H. Huntington, of 

 the New Hampshire Geological Survey, for thin sections of the spec- 

 imens of the syenite, granite, and trap obtained at several of these 

 localities. 



Near Cedar St., Gloucester, the rock is a syenite, while about one- 

 fourth of a mile beyond, at the Rockport road bridge over the rail- 

 road, it is a granite, both of a coarse and fine grained character. 

 Three trap dikes occur here, running respectively north 10° east, 

 north 10° west, and north 60° east, but are somewhat irregular in 

 direction. Beyond this locality, towards Rockport, the syenite pre- 

 dominates, although granite was seen in several places; of a pale 

 red color at one locality. 



North of Rockport the rock is syenite, which extends nearly to 

 the wharf of the Rockport Granite Company, where a gradual pas- 

 sage into granite takes place; the rock along the line of passage 

 contains both mica and hornblende. North of Pigeon Hill the rock 

 again becomes syenite, but a very cursory examination, however, was 

 made there. On account of the blackness of the mica, it often 

 requires careful examination, in the field, to separate it positively 

 from the hornblende, and I have found the test of hardness the most 

 convenient under the circumstances, for the cleavage is often not evi- 

 dent. As. far as my observation has gone, there is no real distinction 

 between the syenite and granite, but they are geologically one and 

 the same rock. The granite, however, appears to run in a band 

 across the Cape, yet the whole subject needs further examination. 



