INTRAFORMATIONAL CORRUGATED ROCKS 609 



a comparatively thick series of thin-bedded, shaly, and calcareous sediments 

 intercalated with beds of pure limestone, now metamorphosed into marble. 

 The thin-bedded sediments are sometimes carbonaceous, sometimes streaked 



with sandy material The limestone-slates are contorted on a minor 



scale. Most of this crumpling was probably due to the intrusion. 



Beyond the last sentence quoted, Spurr says nothing regarding the 

 cause of the intraformational crumpling. The available data 

 rather clearly indicate that these corrugations, like those above 

 described as occurring in northern New York, have been caused by 

 the magmatic intrusion where a block of strata was more or less 

 completely surrounded by the magma and subjected to differential 

 movement, causing the more yielding layers to crumple. 



Between 5 and 6 miles north of Northampton, Massachusetts, 

 the writer has observed excellent examples of local contortions 

 within the Leyden argiUite (Paleozoic) formation near its contact 

 with a basic phase of the Williamsburg granite. For about 2 miles 

 parallel to the contact, irregularly distributed contortions are highly 

 developed in the argillite for 10 to 20 rods out from the contact. 

 Beyond that they rapidly diminish to disappearance. From the 

 field evidence it seems clear that the corrugations resulted from 

 differential movements within the argillite, caused by the shoulder- 

 ing pressure of the rising magma. 



ACTION OF MAGMATIC INJECTION 



In certain regions magmatic injection schists and gneisses con- 

 tain local portions which are highly contorted. Many observations 

 of such phenomena have been made by the writer in his study of 

 the Adirondack Precambrian rocks. The following brief description 

 of a certain district may best serve to illustrate the main principles 

 involved. Extending 2 miles northeastward from just north of the 

 village of Russell, St. Lawrence County, New York, there is a wide 

 belt of mixed rocks containing fine exposures of amphibolite and 

 gametiferous gneisses intimately cut and injected, mostly parallel 

 to the foliation, by moderately coarse-grained granite and pegma- 

 titic granite, the whole mass being conspicuously banded. Just 

 north of the village most of the mixed rock is notably contorted, 

 while one-fourth to one-half of a mile farther east most of the rock 

 is relatively straight-banded, but contains local highly contorted 



