176 THE PHENOMENA OT DRIFT, OR 



occur at all altitudes, from the tops of our highest mountains to 

 the bottom of our deepest valleys ; and what is most remarkable^ 

 is, that the direction of the strice is often the same at all altitudes* 

 It is, indeed, true, that in some valleys we find their course 

 considerably changed ; showing, that at a certain stage of the 

 process, the force was more or less diverted into these valleys, and 

 this is piu-licularly true of the larger valleys, as those of the 

 Hudson, St. Lawrence and Connecticut rivers. But still we 

 find at all altitudes, evidence of the great southeasterly impulse, 

 which has left its traces over the whole breadth of our conti- 

 nent. Nor have I found any certain evidence, that the striae 

 existing at the highest altitudes, are older or newer, than those 

 on the lowest levels. It is true that those examples which 

 appear the freshest and most recent, have been at rather low alti- 

 tude ; such as have been brought to light by removing the soil 

 from the rocks. But at high altitudes I have seen no such un- 

 covering of the rocks. I think, also, that the markings on exposed 

 rocks upon the highest mountains are usually less distinct than 

 in the valleys. But it is also true, that exposed rocks are usually 

 more disintegrated and wasted at great heights than in the valleys, 

 because of the greater extremes of temperature prevailing in the 

 higher regions. It should be borne in mind too, that glacio- 

 aqueous agency has transferred bowlders from very low to very 

 high levels ; and this was the very agency that smoothed and 

 furrowed the rocks. On all these accounts, I hesitate to say that 

 glacio-aqueous agency took place very much earlier on our moun- 

 tains than in our valleys. That there was a long interval between 

 its commencement and its close, and that some of its effects were 

 continued in the valleys longer than upon the hills, I shall en- 

 deavor to show furtlier on. But after all, I am unable to point 

 out which were the earliest and which were the latest of the strice, 

 except in a few limited instances : nor can I say which of the 

 bowlders were transported first, and which last ; except so far as 

 we can judge from their relative vertical position. The fact is, 

 all the phenomena of drift seem to me in a geological sense to 

 be recent. Our tertiary rocks are strewed over with detritus from 

 all the older formations. Why then must we not infer, that the 



