August 20, 1886.] 



SCIENCE. 



157 



nearly due west from the latitude of Bismarck to 

 Tvithin forty miles of the Rocky Mountains, where 

 it curves rapidly to the noi"th, and skirts the moun- 

 tains as far into British America as yet traced. 

 Within the United States the limit of north-east- 

 ern drift barely touches that of demonstrative 

 local glaciation from the Rocky Mountains. West- 

 ward of this, in the valleys of Flathead, Pend 

 D'Oreille, and Osoyoos lakes, and Puget Sound, 

 are deposits of drift regarded as prolongations of 

 the more general drift of British Colutabia, which, 

 if not a continuous mantle, at least passes beyond 

 the character of simple local mountain drift. 

 South of this general drift are deposits of ancient 

 glaciers in the Cascades, Sierras, Rockies, some of 

 the intermediate ranges, and, according to some 

 authorities, the Appalachians. The lacustrine de- 

 posits of the great basin region were correlated 

 with the glacial deposits in time and causation. 



A wealth of significance lies in the sinuosities, 

 vertical undulations, and varying characters of 

 the southern border. It undulates over the face 

 of the land essentially as much as an arbitrary 

 line from New York harbor to Puget Sound, and 

 oould be reduced to horizontality — as it must 

 have been to have marked the margin of some 

 ancient ice- bearing body of water — only by in- 

 credible warpings and dislocations. The border 

 of the drift presents three notable phases ; one 

 part terminating in a thickened belt, a terminal 

 moraine ; another in a thin margin ; and a third 

 in an attenuated border of scattered pebbles. The 

 morainic border prevails in the Atlantic region, 

 and lies on or near the limit as far west as central 

 Ohio, beyond which it retires from it. Through- 

 out the rest of the stretch to the Rocky Mountains 

 the attenuated edges prevail. The latter are 

 thought to represent, one a glacial and the other 

 a giacio-natant action. The attenuated borders 

 are believed to dehmit an earlier ice incursion, 

 and the morainic border a later one, which over- 

 rode the former in the coast region but fell behind 

 it in the interior, having its extension in similar 

 moraines in the interior. 



Corroborative testimony is found in facts drawn 

 from orographic attitudes, drainage, erosion, de- 

 composition, ferrugination, vegetal accumulations, 

 and lacustrine oscillations in the great basin. The 

 interval between the two epochs is measured geo- 

 logically by the cutting down of the beds of the 

 Allegheny, Monongahela, and upper Ohio rivers 

 so me two hundred to three hundred feet, chiefly 

 in rock ; of the upper Missouri River to greater 

 depth ; and by an elevation of the upper Missis- 

 sippi of eight hundred to one thousand feet. Of 

 the earlier drifts, two important subdivisions seem 

 indicated' by present data, and several subordinate 



ones of the later. The distribution of thes^e was 

 outlined. A tliird series of drift sheets, of greater 

 uniformity of material and regularity of deposi- 

 tion, occupying the great basins of the St. Law- 

 rence valley, the Red River of the North, and 

 limited areas of the coast region, and delimited in 

 part by beach ridges, was sketched. The major 

 opinion concerning the oldest series favors their 

 glacier origin, but this opinion is not unanimous. 

 Concerning the second, or moraine-bordered group, 

 opinion is overwhelming that they are du-ect 

 glacier products. Concerning the third series, 

 the weight of opinion favors their subaqueous 

 deposition, either in fringing lakes or in more 

 general submergence. The differentiations of the 

 characters of the three groups were further 

 sketched. Of unstratified bowldery clays or tills, 

 there is the richest variety, ranging through vary- 

 ing combinations of material, texture, and^aggre- 

 gation. Three genetic classes were recognized : 

 1°, subglacial tills ; 2'^, englacial or superglacial 

 tills ; 3°, subaqueous tills ; and 4*^, tills ridged by 

 the thrvist of the margin of the ice. 



Of moraines, terminal, lateral, medial, and in- 

 terlobate varieties are found. The great terminal 

 moraines overshadow all others in interest and im- 

 portance. The distribution of the chief ones were 

 shown upon the map. The Nantucket and Cape 

 Cod moraines were regarded, with more confi- 

 dence than ever, as the equivalents of the Kettle 

 Range of Wisconsin, and the Altamont and Gary 

 moraines of Dakota. Outside of these chief 

 moraines, there are occasional belts of older drift 

 aggregated in the similitude of peripheral mo- 

 raines. Examples are found in central Indiana, 

 western Montana, and the plains of the British 

 Possessions. Back from the two principal ter- 

 minal moraines lie several similar partially deter- 

 mined belts, usually of less prominence and con- 

 tinuity. 



Our most unique moraines are the inter lobate, 

 developed between the tongues into which the 

 great ice sheet of the second epoch was divided at 

 its margin. About a dozen of these, located in 

 half as many states, were recognized ; but only a 

 part present full evidence of true interlobate char- 

 acter. Beautiful lateral moraines abound in the 

 mountainous regions of the west, and some were 

 developed by local glaciation supervening upon 

 the ice retreat of the east. Our medial moi'aines 

 are unimportant, and confined essentially to 

 mountainous glaciation. Allied to the true mo- 

 raines are special forms of aggregation of the sub- 

 glacial debris, among which were enumerated : 

 1°, till tumuli ; 2°, mammillary and lenticular 

 hills ; 3", elongated parallel ridges, trending with 

 the ice movement ; 4°, drift billows ; 5°, crag and 



