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THE DISTRIBUTION OF ANCIENT VOLCANIC ROCKS.
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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.[1] Two years later the detailed work of Diller and Benton established the volcanic character of the felsites of Medford, Melrose, Malden, Sangus, Wakefield and Lynn, and of the amygdaloid of Brighton.[2]

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,[3] but these have not as yet been so carefully examined as those farther north, although Crosby, in his recent "Geology of Hingham," classes the melaphyre. porphyrite, and felsite of Nantasket and Hingham as effusive or volcanic rocks, and describes the latter as "undoubtedly an ancient, devitrified obsidian."[4]

The Middle Atlantic 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

  1. ↑ The Classification of Rocks. Bull. Mus. Comp. Zoöl., 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, 1st ser., Vol. 4, p. 239).
  2. ↑ "The Felsites and Their Associated Rocks North of Boston," by J. S. Diller, Bull. Mus. Comp. Zoöl., 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. 1, 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. 1, Part 1.Occasional Papers of the Boston Soc. Nat. Hist., IV., 1893.
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