GLACIO-AQUEOUS ACTION IN NORTH AMERICA. 167 



true meridian. But such examples are very few compared with 

 those where the same operated southerly and southeasterly. In 

 Europe, as in Switzerland and Scotland, high mountains seem 

 to have formed lines, or centres, from which the bowlders were 

 dispersed in various directions. But in this countiy no such 

 centres have yet been discovered.* The bowlders have been 

 carried obliquely across our highest mountains ; but have, in no 

 case yet known, radiated from them. Indeed, we have reason to 

 conclude that no such case occurs on the continent, unless it be 

 very far to the north ; as I shall endeavor to show further on. 



As a general fact, bowlders are found largest and most numer- 

 ous, nearest to the parent rock from which they have been abraded. 

 Thence they decrease in size and number in a southeasterly di- 

 rection ; becoming also more thoroughly rounded, until at length 

 they are reduced to pebbles and sand. At the distance of many 

 miles from the parent rock, we find the detritus occupying a 

 somewhat wider space than the rock ; but in general, such a 

 divergence is very slight, and the parallelism of the lines along 

 which the bowlders moved is remarkably preserved. 



An important exception to the above statement, respecting the 

 decrease in size of bowlders as we recede from the parent rock, 

 ought here to be noticed. Occasionally and not unfrequently we 

 meet with insulated bowlders, perched perhaps upon the crest of 

 a mountain, or lying in the midst of a deposit of sand, in such a 

 manner as to show that they could not have been pushed along 

 the surface by a vis a tergo, but must have been lifted from their 

 original place and borne along above the surface to their present 

 situation. Such bowlders too must often have been carried across 

 very deep valleys. Indeed, such has been the case with most of 

 the transported bowlders in this country. We are yet without 

 maps sufficiently accurate to give a correct idea of the surface of 



* Febniary, 1S43. Professor Vanttxem, in his able Report on the Third Geological 

 District of New York, just published, expresses a different opinion ; and he refers to Prof. 

 Emmons as having found drift radiating from the high mountains of Essex countjr. But 

 on recurring to Prof Emmons" Report, also just published, I understand that gentleman 

 to refer all accumulations which he considers proper drift, to a northern origin ; and I do not 

 see how the facts subsequently stated in this paper, concerning the White Mountains, 

 can be reconciled with the theory which makes that mountain a centre of dispersion. 



