GEOLOGICAL OUTLINE. 13 



area defined above, and upon it rests, at the lower level of the Connecticut 

 Valley, the complex Bernardston series — conglomerates, quartzites, lime- 

 stone, mica- and hornblende-schists, and gneiss — which is proved by the 

 presence of many fossils to belong in the Upper Devonian. 



A complex series of faults, with much westward overthrusting, bounds 

 the elevated area on the Avest. A series of echeloned faults also drops the 

 bottom rocks of the Connecticut Valley on the east and makes the elevated 

 area a "horst" and the valley bottoms "graben," in the nomenclature of 

 Suess.^ 



A great stock of tonalite, or quartz-dioi'ite, occupies the eastern border 

 of the area and encroaches on the Connecticut Valley. This has come up 

 through the thick Whately amphibolite bed. It graduates westwardly into 

 the gi-anitite, or biotite-granite. This has emerged in the region of the 

 broad Whately limestone bed. This is followed outwardly by a great 

 group of dikes, of every size, of granite or muscovite-biotite-granite. This 

 is in the region of the muscovite-schists without limestone. Each of these 

 rocks seems thus to be distinctly influenced in its chemical constitution by 

 the rocks it has penetrated and dissolved. On the pei'iphery are great 

 quartz veins, and the remarkable tourmaline- and cleavelandite-bearing 

 dikes, with minerals containing rare elements. 



Farther west all the sericite-schists and Cambrian gneisses are free 

 from later igneous rocks except the great isolated granitite dike in 

 Middlefield. 



The A'alley of the Connecticut may in a general way be called a broad 

 syncline, so far as the crystalline rocks are concerned. It is rather a 

 bi'oad area of greater crushing and disturbance, Avhich has favored greater 

 erosion, and over its bottom the crystalline rocks lie often horizontal or 

 in small anticlines and synclines, while on its borders they diji toward 

 the center, often with high angles. In attempting to trace the history 

 of the valley, it will perhaps always be impossible to assign their proper 

 weight to the erosive agencies mentioned above in comparison with 

 another agency which has been of prime importance in the formation 

 of the valley. I mean that which has produced the great faults and 

 the sinking of the areas between the faults. The principal southwest- 



I E. Siiess, Das Antlitz der Erde, Vol. I, pp\ 166, 264. 



