METAMORPHOSED PSEPHITES. 859 



lion, the mineral particles more nearly approach a parallel orientation, 

 instead of a part of them winding- in and out about the more refractory 

 particles. (See pp. 760-762.) Thus, by the granulation and recrystalliza- 

 tion of the pebbles and matrix alike, with the consequent development of 

 schistose and banded structures, a rock is produced to which the term 

 gneiss-psephite or psephite-gneiss is applicable. (See pp. 782-783.) 



Such a rock may be composed in various proportions of any of the 

 minerals which form in the zone of anamorphism, as listed in Chapter Y 

 (pp. 363-364). This follows from the fact that the matrix and the pebbles of 

 the psephites may be derived from all kinds of rocks, from the most basic 

 to the most acid, from the volcanics and the plutonics, and from all varieties 

 of metamorphic rocks. Therefore the rocks may have chemical composi- 

 tions which vary from those of the original igneous rocks to those of mud, 

 in which certain elements, and especially alkalies and alkaline earths, have 

 been depleted. From the great variety of chemical compositions of the 

 psephites it follows that any of the minerals may develop in them which 

 are subsequently spoken of as .forming in the schists and gneisses which 

 belong to the psammite and pelite orders. While there is a very great 

 variety of secondaiy minerals in the schists and gneisses of the psephites, 

 in any given case two or three of these minerals are apt to be preponderant ; 

 and a given psephite-gneiss may be exactly designated by prefixing the 

 names of the chief mineral constituents, as explained on page 783. 



A very characteristic feature of the gneiss-psephites is the parallel 

 orientation of the mineral particles, which gives the rocks cleavage. This 

 characteristic is almost, if not quite, universal with the schists and gneisses 

 which are derived by the metamorphism of sedimentary rocks, and thus 

 serves in many cases as a criterion by which one may separate the original. 

 gneisses of igneous origin from those produced by metamorphism. 



Some of the best known illustrations of schist-conglomerates and 

 gneissq^sephites are those described by Hitchcock many years ago, those 

 of the Hastings district of Canada, 6 those of various places in the Lake 



« Hitchcock, Edward, Hitchcock, Edward, jr., Hager, A. D., and Hitchcock, Charles H., Report on 

 the geology of Vermont, vol. 1, 1861, pp. 28^15. Whittle, C. L., The occurrence of Algonkian rocks 

 in Vermont, and the evidence for their subdivision: Jour. Geol., vol. 2, 1894 ; pp. 422^129. 



& Adams, F. D., and Barlow, A. E., On the origin and relations of the Grenville and Hastings 

 series in the Canadian Laurentian, with remarks by R. W. Ells: Am. Jour. Sci., 4th ser., vol. 3, 1S97. 

 pp. 173-180. 



