Association of American Geologists and Naturalists. 265 



the surface containing them is remarkably homogeneous, even and hori- 

 zontal. On the other hand wherever it consists of harder and softer 

 parts, and where the rock contains imbedded pebbles, or where it has an 

 irregular outline, we may invariably detect a bending, and as it were a 

 free conforming to every inequality on the part of the largest furrows 

 and the minutest strias. Lastly, where there is much disparity in the 

 hardness of the different parts of the eroded surface, there will be ob- 

 served a little ridge of the softer portion lying to the southeast or on the 

 lee side of each harder knot or pebble, round which the strife sweep 

 and meet upon the ridge or tail, precisely as water parts at the prow of 

 a ship and coalesces beyond the stern. 



2d. Respecting the drift itself, the following appear to be the princi- 

 pal phenomena : 



Throughout all the northern tracts of the United States and the ad- 

 joining districts of the British provinces, the surface is covered with a 

 loose stratum composed of sand, clay, gravel and bowlders of all sizes, 

 variously mingled and locally stratified. 



The stratification is characterized by plains of inclined and confused 

 deposition, denoting turbulent currents. 



The materials invariably belong to formations lying north or north- 

 west of their present positions, and great spaces occupied by broad 

 plains, wide belts of hills and even mountains, deep valleys, and vast 

 sheets of water, intervene. The bowlders have evidently not radiated 

 from any local centres of dispersion. 



The southern margin of the continuous drift stratum reaches in the 

 east to Long Island and northern Pennsylvania, and in the west to the 

 Ohio river ; but its gravel extends along the immediate valleys of the 

 Delaware, Susquehanna and Mississippi, to points much further south. 



The direction of the transport of the drift is in each district coinci- 

 dent with that of the scratches. 



The size of the rolled fragments progressively declines as we recede 

 from the parent rock southward or southeastward, and though solitary 

 blocks of large dimensions lie in and upon the general stratum, where 

 the imbedding matter has only the coarseness of gravel or sand, yet 

 even there these bowlders obey the general law of a rapid diminution 

 of size towards the south. 



In wide and level districts, the bowlders are often strewed uniformly 

 over great spaces of country. In other places, more especially at the 

 base of plateaus or terraces, and opposite to gorges and prominent crests 



