GLACIO-AQUEOUS ACTION IN NORTH AMERICA. 203 



my mind by an examination of their outlines. When they are 

 composed of sand and gravel, and have steep sides, it seems im- 

 possible that every powerful rain should not wash away some 

 portion of them and convey it to the bottom. Yet it is rare to 

 see in the cavities between them much accumulation of alluvial 

 matter. A random estimate would imagine a greater change of 

 this sort in a few centuries, than has actually taken place in the 

 thousands of years that must have passed since the moraines 

 were piled up. 



Another inference of importance has been forced upon me 

 from the same facts. When I see these moraines around the 

 base, and on the flanks of mountains, retaining the very shapes 

 which they took when first produced, I cannot believe that those 

 mountains have been elevated since that time. If they had been, 

 how is it possible that loose and steep hills of gravel, should not 

 have been disturbed and crumbled down, as they have been by 

 the upHfting of the Alps ? If the northern part of our country, 

 therefore, has experienced vertical movements since the glacio- 

 aqueous epoch, it must have been as a whole : for local eleva- 

 tions to much extent are out of the question. 



It is only recently that moraines have been described by geol- 

 ogists as a part of the phenomena of drift. Nine years ago, I 

 described those of Massachusetts in that connection, and gave 

 sketches of some of the most remarkable cases in my Report on 

 the Geology of that State, published in 1833. But as I saw in 

 the writings of European geologists only slight notices of such 

 phenomena, I feared that I had mistaken their character, until the 

 papers of Agassiz, Bucldand, and Lyell, were read before the 

 London Geological Society, on the marks of glacial action in the 

 north of England and in Scotland. I then perceived that these 

 appearances were precisely the same on both sides of the Atlan- 

 tic : and the introduction of the agency of ice into geological 

 dynamics, is beginning to throw light into this hitherto dark and 

 untrodden field. 



