1882 .] 
875 
[Davis. 
more in detail. Glacial deposits are so varied in all their charac- 
ters, and so irregularly disposed in form, structure and thickness 
over the rock foundation on which they rest, that undrained 
hollows necessarily result. Such basins may be separated into 
subspecies according as the drift that bears them is in the 
form of boulder clay, moraine, kame, or sand-plain, but it is 
not to be expected that these subdivisions are limited by hard 
and fast lines ; they constantly run into one another, and into the 
Drift Barrier Basins as well. 
1. The surface of boulder-clay, lower till or ground-moraine of 
unstratified drift, is generally too well concealed by stratified drift 
above it to find basins determined by its form alone; but in 
Northern Minnesota 1 there are many lakes more dependent on 
this origin than any other, and doubtless others as numerous will 
be found in British America when the region is visited by 
observers having this point in view. Such lakes are small and 
shallow, and not of very irregular outline. In some regions the 
ground moraine attains an exceptional and very variable thick- 
ness in the form of drums, drumlins, whalebacks or lenticular 
hills (as these drift masses are called in Scotland, Ireland, New 
Brunswick and New England), and then, aided by other forms 
of detritus, they may catch ponds. 2 Some such irregularity of 
ground moraine combined with stratified drift is the cause of the 
countless ponds in the Pays de Dombes in France, northeast of 
Lyons, 3 and the many ponds and bogs (filz, ried, moos) on the 
drift from Lake Constance to Munich and beyond. 4 
1 W. Upham, Geol. Surv. Minn. Report for 1879. 
2 Some lakes in Northwestern Ireland are probably of this origin : see Kinahan 
and Close, The general glaciation of Iar-Connaught, Dublin, 1872; and Kinahan, Val- 
leys, 110. 
3 Falsan et Chantre, Soc. Gdol. Bull, xxvi, 1868, 374, and Monograph ie gdol. des 
anciens glaciers . . . . du bassin du Rhone, Lyon, 1879. See Carte de France de l’Etat 
Majeur, sheet 159, copied in Reclus, La Terre. For the Jura, see Ch. Martins, Obs. 
sur l’origine glaciaire des tourbieres du Jura neuchatelois; Montpellier, Acad. Mem., 
viii, 1871, 6. 
4 C. W. Giimbel, Geogn. Karte des Konigreichs Bayern, sheets ii, in, iv, v. F. 
Stark, Die Bayerischen Seen und die alten Moranen, Deutsche Alpenverein Zft., 1873, 
67-78, 72. Kinkelien, Senckenberg. Gesell. Bericht, 1875, 96. Zittel, Mijnchen, Akad. 
Sitz’b. iv, 1874, 259. Probst, Wurtemberg. Jahresh. xxx, 1874, 59. 
