860 A TREATISE ON METAMORPHISM. 



Superior region," and those of Hoosac Mountain, western Massachusetts. 6 

 In each of these localities, where the mashing was not so severe as the 

 average for the formation, the rocks are not metamorphosed beyond the 

 stage of schist-conglomerate, and thus give evidence that the gneiss- 

 psephite continuations of these rocks have been produced from sediments. 

 One of the very best illustrative localities is that of the Vermont 

 formation of Hoosac Mountain, described by Wolff. In this formation 

 every stage of gradation from a distinct and unmistakable schist-conglom- 

 erate to gneiss may be seen. Another excellent illustration which shows 

 intermediate stages between the conglomerate and the gneiss is that of 

 the Sturgeon River tongue of the Crystal Falls iron-bearing district of 

 Michigan/' Here the matrix is completely recrystallized, and if it were 

 not for the pebbles would be unhesitatingly called a gneiss. But the 

 pebbles are in an intermediate stage of destruction, being considerably 

 flattened, though still very distinct. The upward continuation of this for- 

 mation, in which the fragments were small, shows no evidence whatever, 

 by texture or structure, of its original clastic character, either in the field 

 or under the microscope. It is a completely recrystallized quartz-feldspar 

 sand which has become a psammite-gneiss. (See pp. 875-876.) 



PSAMMITE OEDEE. 



QUARTZ-SAND FAMILY. 



The quartz-sand family (PI. IX) includes quartz-sand rock, sandstone, 

 quartzite, and schist-quartzite. 



QUARTZ-SAND ROOK. 



Quartz-sand rock is an unconsolidated deposit or formation composed 

 mainly of grains of quartz. Quartzose sands are one of the most common 

 and widespread of the mechanical sediments. The origin of such sands is 

 so well understood that little need be stated as to this part of the subject. 



8 Van Hise, C. K., and Bay ley, W. S., The Marquette iron-bearing district of Michigan, with a 

 chapter on the Bepublic Trough, by H. L. Smyth: Mon. U. S. Geol. Survey, vol. 28, 1897, pp. 294-298, 

 434-^37, 477-479. Clements, J. Morgan, and Smyth, H. L., with Bayley, W. S., and Van Hise, 

 C. R., The Crystal Falls iron-bearing district of Michigan: Mon. U. S. Geol. Survey, vol. 36, 1899, 

 pp. 474-^76. 



''Pumpelly, Baphael, Wolff, J. E., and Dale, T. Nelson, Geology of the Green Mountains in Mas- 

 sachusetts: Mon. IT. S. Geol. Survey, vol. 23, 1894, pp. 48-59. 



o Wolff, cit., pp. 48-59. 



dMon. U. S. Geol. Survey, vol. 36, cit., pp. 474-476. 



