102 GREEN MOUNTAINS IN MASSACHUSETTS. 



white gneiss-conglomerate of Hoosac mountain is the Cambrian quartzite 

 (Vermont). 



GENERAL CONCLUSIONS. 



In the previous pages a presentation of the facts observed has been 

 attempted without drawing conclusions or stating results. A brief sum- 

 mary is therefore here introduced. 



The rocks of Hoosac mountain consist of quartzites, conglomerates, 

 gneisses, limestones, schists, and amphibolites. In all these rocks there is 

 abundant evidence that some elements have been crushed by great pres- 

 sure; the large broken microcline and quartz masses of die coarse gneiss 

 and the pebbles of the conglomerate show this, and this crushing has 

 been accompanied by chemical action which has formed new feldspar, mica, 

 and quartz. With the exception of the pebbles of the conglomerates, it is 

 with great difficulty that we recognize the remains of detrital material, and 

 yet a large part of the series is of detrital origin. The rocks as we now 

 find them are thoroughly metamorphic, and vet we feel sure that the 

 material for the present rocks must have come from the old sediments. To 

 trace the process of change is a problem of the future. If, as this work indi- 

 cates, these rocks are simply the Cambrian and Silurian sandstones, lime- 

 stones, and shales, altered by a metamorphism increasing from the Hudson 

 river eastward, then careful petrographic studies along an east to west 

 line ought to solve this problem. A partial investigation of some of the 

 rocks of Mount Greylock, made by the writer, shows the great similarity 

 between the metamorphic rocks of Hoosac mountain and of Greylock, 

 qualitatively considered, but in quantity the difference is striking. There 

 are no coarse gneisses on Greylock, and it is only locally that fine-grained 

 banded gneisses are found, but limestones, quartzites, and schists (or phyl- 

 lites) abound, and we must again state the absolute lithologic identity of 

 these varieties with those of Hoosac, The schists of Mount Greylock and of 

 the Taconic range have the same crystals of albite and the same ottrelite; the 

 limestone of Greylock is feldspathic, just like that at the base of Hoosac. It 

 is then a suggestion worth considering whether the metamorphism does no* 

 increase as we go downward as well as eastward. The schists of Grevlock 

 and those of Hoosac at the top of the series are alike; the coarse gneisses 



