596 WILLIAM J. MILLER 



with the slow-moving magmatic currents. According to this view, 

 individual large blocks or belts of Grenville strata, or several such 

 blocks or belts separated by intrusive masses, with strike of intru- 

 sive masses parallel to Grenville stratification, would be expected 

 to show monoclinal dips ; some Grenville masses were shifted around 

 in irregularly rising magmas so as to show various strikes according 

 to directions of movement of the magmas, and hence would not be 

 expected to exhibit monoclinal dips; some Grenville masses were 

 merely domed over bodies of rising magma and would exhibit more 

 or less quaquaversal strikes and dips; while still other Grenville 

 masses were probably bent or even considerably folded into syn- 

 clines by being caught between bodies of magma upwelling at about 

 the same rate. Isoclinal or close folding on a large scale would 

 scarcely be expected. 



In all of this discussion it is important to bear in mind that the 

 Adirondack intrusives occupy a much greater extent than the 

 invaded Grenville rocks, and that, in spite of their intrusive char- 

 acter, they everywhere seem to occupy the position of a fundamental 

 or underlying gneiss. It appears to have been literally true that 

 the Grenville strata were irregularly floated on a vast body of 

 magma, the magma in many places having either arched up or 

 broken through the strata. 



ORIGIN OF GRENVILLE FOLIATION 



We have just shown that the Grenville strata have never been 

 highly folded or compressed. It is therefore necessary to explain 

 the metamorphism of the strata on some other basis than that of 

 subjection to severe lateral pressure. The old sediments are thor- 

 oughly crystallized, and it is certain that they have been reorganized 

 into new minerals under deep-seated conditions; that is to say, 

 they have undergone anamorphic metamorphism. But evidently 

 we are here dealing with a case of essentially static, rather than 

 dynamic, metamorphism. 



Origin of parallelism of Grenville foliation and stratification. — 

 The universal parallelism of Grenville foliation and stratification 

 is a fact of prime importance. If the Grenville and accompanying 

 great intrusives had been subjected to compression severe enough 



