136 



GftEEE MOUNTAINS IN MASSACHUSETTS. 



topographic features will bo noticed at the end. The area covered by the 

 mountain, as thus defined, measures 16i miles by about S\ ; that is, about 

 53 square miles. If the short intervening range of East and Potter mount- 



Greylock SacLtleBaUSiu/arZoaf: East Alt. 



*J}ench tit Srjid .Form.Sbp. Cole. Schist. 





Fig. 30.— Sketch of Mount Greylock, " Saddle mountain." north-northwest side, from the U. S. I '"Mst Survey station, on 



Mount Equinox, in Vermont about 35 miles distant, showing the depression oorres] ling to tin- great trough in tin cen 



tral syncline, and the bench at thesouth end of themass,due to tin- Bellowspipe limestone horizon (shown by 2 birds) 

 Owing to the direction of the view the mountain appears much foreshortened. 



ains be included (and structurally it belongs to the Greylock mass), the' 

 mountain area would measure about 85 square miles. 



STRUCTURAL. 



This entire area consists of a few kinds of metamorphic rocks: lime- 

 stone, more or less crystalline and micaceous, quartzite, and schists — 

 chloritic, feldspathic, pyritiferous, plumbaginous, calcareous. In the val- 

 leys, and along the lower and less inclined portions ot the hills these rocks 

 are covered with drift. 



The key to the geologic structure of Mount Greylock is an under- 

 standing of the relations of cleavage and stratification and the relation of 

 these to the pitch of the folds. 1 



There are large areas, sometimes half a mile square, where the only 

 foliation presented by the outcrops is of secondary character and where no 



' Although Professor Eaton, in liis section of 1820, indicates cleavage on theTaconic range, its 

 importance seems to have been overlooked \>\ liis successors in the stud; of this region. 



