THE DISTRIBUTION OF ANCIENT VOLCANIC ROCKS. 25 



accompanying fragmental materials were the products of ancient 

 volcanic action. He maintained that the felsites of Marble 

 Head were merely altered rhyolites which had once been quite 

 like those of the western Cordilleras ; and their banding was flow- 

 structure ; and that they were accompanied by ash beds which 

 he called porodites.'^ Two years later the detailed work of Diller 

 and Benton established the volcanic character of the felsites of 

 Medford, Melrose, Maiden, Sangus, Wakefield and Lynn, and of 

 the amygdaloid of Brighton.^ 



Other areas of similar rocks occur near Newburyport, and 

 also to the south of Boston at Needham, Dedham, Milton, Blue 

 Hill, Hingham, Nantasket and Manomet,^ but these have not as 

 yet been so carefully examined as those farther north, although 

 Crosby, in his recent " Geology of Hingham," classes the mela- 

 phyre. porphyrite, and felsite of Nantasket and Hingham as 

 effusive or volcanic rocks, and describes the latter as "undoubt- 

 edly an ancient, devitrified obsidian." 4 



Tlie Middle Atla^itic States. — In New York state there are, 

 as far as the writer is aware, no remains of igneous rock which 

 have solidified at the surface. Nevertheless, the isolated and 



^ The Classification of Rocks. Bull. Mus. Comp. ZooL, Harvard Coll., Vol. 5, p. 

 282, 1879. It is worthy of note, in view of all the erroneous ideas that have prevailed 

 regarding the Boston felsites, that as early as 1822, Dr. Thomas Cooper, President of 

 the College of South Carolina, in an article on "Volcanoes and Volcanic Substances" 

 says : " 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." 

 (Am. Jour, of Science, ist ser., Vol. 4, p. 239). 



^ " The Felsites and Their Associated Rocks North of Boston," by J. S. Diller, 

 Bull. Mus. Comp. ZooL, Vol. VII., p. 165, 1881 ; and "The Amygdaloidal Melaphyre of 

 Brighton, Mass.," by E. R. Benton, Ph.D., Proc. Bost. Soc. Nat. Hist., Vol. 20, pp. 

 416-426, 1880. The writer is indebted to Mr. Diller for the privilege of examining 

 his collection of slides of the Boston rocks which are in all essential respects identical 

 with those from the coast of Maine, from South Mountain and North Carolina. 



3 E. Hitchcock: Final Report on the Geology of Massachusetts, Vol. i, p. 150, 

 1841 ; W. O. Crosby : Geology of Eastern Massachusetts, pp. 79-95> 1880. 



4 Proc. Bost. Soc. Nat. Hist., Vol. 25, p. 502, 1892. See also by the same author : 

 The Lowell Free Lectures on the Physical History of the Boston Basin, 1889 ; and the 

 Geology of the Boston Basin, Vol. i, Part i. Occasional Papers of the Boston Soc. 

 Nat. Hist., IV., 1893. 



