THE DISTRIBUTION OF ANCIENT VOLCANIC ROCKS. 9 



by the adherents to the so-called metamorphic school, like Dana, 

 Logan, Rogers, Lesley and Winchell, who fail to find among 

 the ancient foliated crystallines anything beside altered sedi- 

 ments, but perhaps even more by the influence of that most 

 extreme of all Wernerians, Dr. T. Sterry Hunt. While antithet- 

 ically opposed to the members of the metamorphic school in his 

 notions of lithological character as an index of geological posi- 

 tion, Dr. Hunt had in common with them the conviction that the 

 ancient lavas and volcanic breccias, tuffs and ash-beds were 

 normal aqueous deposits. The basic volcanics of eastern North 

 America enter so argely into his " Huronian," and the acid 

 types so largely into his " Arvonian," that his writings may still 

 be used as suggestive of localities where ancient effusive rocks 

 may be sought for.^ 



But there have not been wanting those among the earlier 

 American geologists who have clearly recognized the igneous 

 members of the ancient crystalline formations, in spite of their 

 disguised character. Prominent among them are E. Hitchcock, 

 Emmons, Lieber, Foster and Whitney. Not only the igneous, 

 but the volcanic (surface) character of the Lake Superior lavas 

 has been maintained by Pumpelly,^ Wadsworth,3 Irving,'^ Van Hise^ 

 and the present writer.'' In Canada igneous rocks have always 

 been regarded abundant in the oldest formations, while the 

 volcanic character of some of them has been insisted on by 

 Selwyn ^ and mentioned by other members of the Canadian Geo- 

 logical Survey. A looseness of usage is, however, observable in 

 some of these reports, where "volcanic" is made synonymous 



^ See : Presidential Address, Am. Assn. Adv. Sci., 1871 ; Proc. Am. Assn. Adv. 

 Sci., 1876, p. 2II-2II ; Azoic Rocks, 1878; Am. Jour. Science, May, 1880 ; Mineral 

 Physiology and Physiography, Chap. IX., 1886. 



^ Geology of Michigan, Vol. i, 1873. 



3Bull. Mus. Comp. Zool., Vol. 7, p. iii, 1880. 



4 Monograph V., U. S. Geological Survey, 1883. 



5 Bull. Geol. Soc. Am., Vol. 4, p. 435, 1893. 



«Bull. U. S. Geol. Surv., No. 62, p. 192, et seq., 1890. 



7 Report of the Geol. Survey of Canada for 1877-78. A, p. 5. Trans.. Roy. Soc. 

 of Canada, Vol. i, p. 10, 1882. 



