THE DRIFT-DEPOSITS OF THE NORTHWEST. 207 



JVb. 3. The great deposit that follows No. 2, whether it be of clay 

 or of gravel and sand, is that designated in common usage " hard- 

 pan." It constitutes the chief member of the drift throughout the 

 Northwest. It is rarely found entirely wanting, whereas the foregoing 

 are very often wanting. It seems to be the parent member of which 

 the former two are offshoots, or modifications. It sometimes has a 

 thickness of more than two hundred feet, and rises to the surface form- 

 ing the basis of the soil. It consists of a heterogeneous mixture of 

 clay and gravel-stones, with bowlders of northern origin. It is nearly 

 impervious to water, and occasionally, but rarely, shows a rude ar- 

 rangement in alternating bands, as if, in a plastic state, it had been 

 folded upon itself. Such arrangement discloses no assortment of the 



Fig. 2. 



NATURAL SURFACE. 



ZvW&&c 



-ttXsVv-:-- r- 



Section of the Drift at the Falls of St. Anthony. 



a. " Bluff- formation," alluvial, unstratified, mostly sand 6- 8 feet. 



b. Stratified, fine sand 6-20 do. 



c. Gravel and stones, in isolated pockets, unstratified. 



d. Bowlders and gravel, the former distinctly glaciated. 



e. Hand pan, or " unmodified " drift seen 10 do. 



/. Massive, fine sand. 



g. Rude arrangement within the hard-pan. 

 h. Sandy and stony, with rude stratification. 

 i. Hid from view by sliding sand. 



materials that can be likened to the assortment seen in No. 2. The 

 bowlders embraced in this member of the drift almost invariably show 

 glaciated surfaces. Although apt to be more abundant near the bot- 

 tom of the deposit, they are not confined to it, as is sometimes stated, 

 but occur throughout the whole. This deposit of hard-pan sometimes 

 encloses lenticular masses of assorted materials. It has even been seen 

 to overlie a considerable thickness of fine stratified sand the extent of 

 which could not be ascertained. In general, however, it is one com- 

 pact, uniform mass, varying slightly in the proportions of its different 

 parts, from State to State, according to the readiness of supply of any 



