4:66 F. H. Lahee — Metamorphism and Geological Structure. 



(fig. 11), is suggestive, not of interference by the dikes, as if 

 already present, but of pressure exerted against the cleavage 

 by the force of the incoming intrusive.* (7) Except in one 

 doubtful instance, the stratification, wherever discernible, is 

 regular and not contorted. We admit, however, that, where 

 the cleavage is crumpled, the bedding laminge also must have 

 suffered some minor deformation ; but there are faint indica- 

 tions that both cleavage and stratification, when folded as well 

 as when relatively plane, are approximately coincident. 



From these statements we infer that the intrusion of the 

 dikes — at least of those on the Bonnet — was chiefly subsequent 

 to the deformation of the enclosing Carboniferous sediments. 



Conclusions to the study of the acid intrusives. — In regard 

 to the Acid Intrusive Series, we conclude: (1) that, since 

 endomorphic and exomorphic metamorphism are slight, the 

 intrusion was weak ; (2) that, since the granite sometimes has a 

 conspicuous gneissic structure, it was injected while the forces 

 that caused the folding of the country rock were still active ; 

 (3) that, since the pegmatite shows at most only slight crush- 

 ing, its dikes entered in general toward the close of the period 

 of deformation ; (1) that, since the quartz veins are not 

 dynamically metamorphosed, they were injected after deforma- 

 tion was at an end ; (5) that, since injection of the Acid In- 

 trusive Series, initiated during the process of folding, was not 

 completed until after the close of this process, and, since the 

 quartz veins are a differentiation product of the pegmatites, 

 while the pegmatites, in their turn, are a differentiation 

 product of the granite, therefore, the period of intrusion must 

 have been of long duration ;f (6) that, since the processes of 



* Compare Bastin, speaking of the Maine pegmatites : "The bending of 

 the schist folia in the manner shown indicates also that the pegmatite when 

 intruded behaved to a certain extent like a solid body capable of exerting 

 differential thrust on the inclosing walls of schist." (Bastin, E. S., Geology 

 of the Pegmatites and Associated Eocks of Maine, U. S. G. S., Bull. 445, 1911, 

 p. 34.) 



f Accurate statements of the relative ages of folding, intrusion of acid 

 rocks, and production of metamorphism in regions where these phenomena 

 occur, are rare in the geological literature. The following may be men- 

 tioned : G. O. Smith and F. C. Calkins described schists cut by granodiorite 

 and by pegmatites which were somewhat gneissic. (A Geological Eeconnais- 

 sance across the Cascade Eange near the 40th Parallel, U. S. G. S., Bull. 

 235, 1904.) E. S. Bastin held that the schist of Boothbay Harbor, Maine, 

 has been intruded by granite and related pegmatite later than deformation 

 and metamorphism. (Quartz and Feldspar Deposits of Maine, U. S.'G. S., 

 Bull. 315, 1906, p. 384.) From studies in various localities, W. O. Crosby 

 wrote, "In every instance the pegmatite is clearly younger than the foliation 

 of the enclosing rocks." (Crosby and Fuller, op. cit., p. 339.) E. A. Daly 

 mentioned phyllites cut by quartz veins which seemed to have shared in the 

 crushing, but most of which were later. (The Geology of Ascutney Moun- 

 tain, Vt., U. S. G. S., Bull. 209, 1903, p. 15.) In his 'Granites of Maine 

 (U. S. G. S., Bull. 313, 1907), T. N. Dale said of the Waldoboro quarry, 

 "The granite sends small apophyses into the schist and also contains inclu- 



