250 Address before the Association of American Geologists. 



which are six thousand two hundred and thirty four feet high ; 

 although the nature of the rock there, is most unfavorable for 

 preserving furrows and markings. 



Thirdly, the smoothing and furrowing of the rocks exhibits 

 almost equal freshness at all altitudes, which indicates an ap- 

 proach to synchronism in the producing cause. 



Fourthly, the almost perfect parallelism preserved by the 

 grooves and scratches over wide regions, shows that they were 

 made by the projecting angles of very large and heavy masses of 

 great extent, moving over the surface with almost irresistible 

 force, by water or some other mighty agent. There is sometimes 

 more than one set of scratches, which intersect one another at a 

 small angle, as has been shown by Prof Locke to occur in Ohio, 

 but each set preserves its parallelism most perfectly. Even where 

 they pass over high and precipitous ridges, they are rarely turned 

 out of their course. 



Fifthly, this agency appears to have been less and less power- 

 ful as we go southerly. We have as yet, indeed, had but few 

 trusty reports on this subject from the southern portions of North 

 America ; but had the phenomena of drift been as striking there 

 as in New England, New York and Canada, they would certainly, 

 ere this, have been described. It ought not to be forgotten, how- 

 ever, that De la Beche has described the drift of Jamaica as very 

 similar to that of New England. 



Sixthly, the relative levels of the surface have not been essen- 

 tially changed by vertical movements, since the epoch in which 

 this agency was exerted. They could not have been much 

 changed without disturbing the detritus, often fancifully arranged 

 in the valleys and on the flanks of the hills ; nor without some- 

 times breaking up the smoothed and furrowed surfaces of the 

 rocks along their joints or planes of stratification. But such a 

 disturbance I have never witnessed. 



Seventhly, the North American continent must have attained 

 essentially, its present height above the ocean, previous to the ex- 

 ertion of this agency. For all our formations, as high at least as 

 the eocene tertiary, are covered with drift ; and I know of no ev- 

 idence of any important uplift subsequent to that which has tilted 

 up our tertiary strata. This work, therefore, could not have been 

 accomplished while the continent was beneath the ocean. Other 

 evidence of this position might be adduced, did time permit. 



