THE CRYSTALLINE KOCKS NEAR ST. JOHN, N. B. 23 



Erosion and Folding. 



Let us now suppose that in the area we are discussing 

 the slow sinking of the crust stops, and a slow elevation 

 begins. The sediments last deposited will be raised out 

 of water, eroded by air and rain, and carried oiF by the 

 streams to some other region. As the elevation and 

 erosion continue, strata will be exposed at the surface, 

 which are more and more altered. In the course of time 

 the rocks overl^dng our granitic intrusion will be all 

 swept away, and we will have the granite (with a zone of 

 altered rocks around it) brought to the surface. As time 

 went on, yet more of the surface rock would be carried 

 oif, till finally we would have brought to light the most 

 highly altered rocks, scarcely distinguishable from the 

 granite itself. As all these rocks successively come 

 to the surface their minerals are altered and destroyed 

 hy air and rain, and the new minerals formed, with the 

 remnants of the old, are swept away, carried off and 

 deposited as sediments in some other area, there to 

 undergo the same cycle of change that has been already 

 outlined. 



From causes which as yet are not well understood, 

 the upper crust of the earth has been folded and w^rinkled 

 — like the skin of a dried apple, to use an old comparison. 

 The immediate cause of this folding seems to be a side 

 thrust or pressure coming from that part of the crust 

 which underlies the great oceanic areas. The crests of 

 the folds are iirst exposed above water and are rapidly 

 eroded ; the hollows are slowly worn away, or, if under 

 water, are tilled up by later sediments, which in their 

 turn are folded and squeezed together by the ocean 

 thrust. The strata arc thus exposed more or less on 

 edge, instead of flat-lying ; and this up-tilting is most 



