FORMER GLACIATIOX OF NORTHEASTERN AMERICA. 377 



we have therefore almost exactly the reverse, — a condition of things which 

 greatly enhances the difficulty of getting a generally recognized starting- 

 point from which to proceed to a co-ordination of the drift of this country with 

 the glacial formations of Europe. 



Omitting for the present the consideration of the striation in the Northern 

 Drift region, we may examine, first, the nature and distribution of the detri- 

 tal material, the origin of which has been the object of so much discussion 

 among American geologists during the past forty years. Complicated as are 

 the phenomena by which this material has been brought into its present 

 position, and various as are its lithological aspects, there are certain featiu'es 

 of its occurrence which are thoroughly characteristic, and which may be con- 

 sidered, to the exclusion of those local peculiarities which are not of special 

 importance in the present connection. 



The Northern Drift of Northeastern America consists, in general, of un- 

 consolidated detrital material lying on the surface, a portion of which detritus 

 is found on examination to have been brought from more northerly regions. 

 The movement has not often been in a precisely meridional direction ; but 

 it has, on the whole, been from some more northerly point towards a south- 

 erly one. The nature of this transportation is, in general, as follows : Start- 

 ing from an outcrop of some easily recognized rock, we find that fragments 

 of it have been carried southerly for a considerable distance, and that, as a 

 rule, these fragments grow smaller and become more thoroughly water-worn 

 as we recede from the place of their origin. Taking a mass of detritus at 

 any point, we find, in most cases, that it is largely made up of material simi- 

 lar to that occurring in siiii close at hand, with a certain admixture of other 

 materials brought from regions farther north, and often from a great distance 

 in that direction. 



The character of the deposits conmionly included under the general name 

 of drift by American geologists is extremely varied. Over a large part of the 

 eastern portion of the Drift region the predominating material is what may 

 properly be called gravel, made up of fi-agments of rock of moderate size, and 

 almost invarijibly thoroughly water-worn. Most of this gravel is more or less 

 distinctly stratified, and with it are associated frequent beds of sand of various 

 degrees of fineness. These intercalated deposits of sand often exhibit cross- 

 stratification in a very marked degree. The lower we descend, and as we 

 approach the level of the streams in the larger valleys, the finer, as a rule, 

 the material becomes. In such positions brick-eartha and clays, often very 



