182 GIIEEN MOUNTAINS IN MASSACHUSETTS. 



Williamstown, 1 also the presence of galena and zinc blende here and there 

 in small quantities. 



Prof. E. Hitchcock gave five analyses of the limestone of this horizon, 

 which show it to be in places a dolomite. 2 



In the upper part, near the overlying schist, occur irregular deposits 

 of limonite, as at Cheshire, and along the north side of Mount Prospect, 

 and on the east side of Potter mountain. 3 Prof. Dana has fully explained 

 the origin of these iron-ore beds. 4 



Towards the upper part of the limestone occur also strata of quartzite; 

 thus on the east side of the extreme end of the Greylock schist mass near 

 Pittsfield, and also near the Adams quarries. 



The fossils found by Mr. Walcott, and already referred to, came from 

 this horizon, but fossils seem to be exceedingly rare. 5 



The structural peculiarities of the rock are its almost universal flexure 

 into minor pitching folds, and, as already explained (p. 157), its not infrequent 

 minute plications, and also its cleavage sometimes obliterating all trace of 

 stratification. 



THE BERKSHIRE SCHIST. 



This consists of the lower sericite-schists. The groundmass of these 

 schists is made up of interlacing fibers of muscovite (sericite) and folia 



1 Geology Second District. New York, 1842, p. 158. 



2 Final Report Geology of Massachusetts, 1841, p. 80. 81. 



3 At the latter place (Laneshoro Iron company's ore bed) the ore occurs in two positions. In one 

 place, owing to an overturn, it lies below the limestone and above the schist. In another it lies on 

 the upper side of a small limestone anticline, the schist capping having been eroded. In another 

 place a reddish, partially decomposed schist overlies the limestone, the ore probably occurring 

 between. The stratigraphic position of the ore is identical in all these cases, however. On the 

 schist side of the ore there is usually a mass of mottled clay, probably originating in the decomposi- 

 tion of the schist, and on the limestone side a yellowish ochre. Manganese ore (pyrolusite) occurs 

 here associated with the iron ore (limonite). 



'Am. Jour. Sci., 3d ser., vol. U, 1877, p. 132. 



Berkshire geology in "Four papers of the Berkshire Historical and Scientific Society,'' published 

 by the society, Pittsfield, June 1, 1886, p. 19. 



Much of interest in reference to these Silurian limonites will be found also in vol. 15 of the 

 Tenth Census (1880), Washington, 1886, especially in the introductory chapter by Prof. Raphael 

 Pumpelly on the geographical and geological distribution of the iron ores of the United States (p. Id, 

 on the limonites), and also in Mr. Bayard T. Putnam's notes on the samples of iron ore collected in 

 Connecticut and Massachusetts, p. 87. 



Since the completion of the manuscript the writer has found crinoid stems in the upper part of 

 the limestone on Quarry hill, New Ashford. 



