LAFAYETTE FORMATION AND SASKATCHEWAN GRAVELS. 91 



where the streams expanded over broad areas with shallow and slack- 

 ened currents. As the elevation increased, however, the rivers would 

 attain steeper sloi)es and finally erode much of the deposits which they 

 had previously made. During the culmination of the uplift, producing 

 the northern ice-sheet, Chesapeake and Delaware bays were excavated 

 and erosion was in progress at a far more rapid rate than with the 

 present low altitude of this region. 



According to this view we may compare the Lafayette formation 

 with the Indo-Gangetic alluvial plain, which stretches along the south 

 side of the Himalayas from the Indus to the Ganges, covering about 

 300,000 square miles and forming the richest and most populous portion 

 of India. This plain rises from the sea level to an elevation exceeding 

 900 feet. Its prevailing formation is fine silt or clay, more or less sandy, 

 with gravel near the borders of the plain. The central portions have a 

 thickness of at least 400 to 700 feet, as determined by borings which do 

 not at these depths reach the bottom of the alluvium ; and this entire 

 deposit, according to Medlicott and Blanford, is of Quaternary age and 

 of fresh-water origin, having been laid down by the flood stages of the 

 rivers that descend from the very rainy southern slopes of the Hima- 

 layan range.* 



In the Nelson river basin a gravel and sand formation which appears 

 to be the equivalent of the I^afayette, both in its relationship to the 

 glacial drift and in the conditions of its deposition, is found by Mr R. G. 

 McConnell to have a wide distribution upon the portion of the north- 

 western plains drained by the South Saskatchewan river and its tribu- 

 taries. It also is known to extend to branches of the Missouri and of 

 the North Saskatchewan. ISIr McConnell writes : 



Under the general name of the South Saskatchewan gravels are included the 

 pebble conglomerates and incoherent gravels and siLty beds which are found, as 

 valley or lake deposits, in different parts of the district, and which, although desti- 

 tute of organic remains so far as examined, are known by their relative position 

 to be intermediate in age between the Miocene and the Quaternary, and to belong 

 mostly to the period immediately preceding the latter. They are, however, not 

 all contemporaneous, and in one or two places afford evidence by the admixture 

 of Laurentian and quartzite pebbles toward the top of a gradual blending with the 

 lowest glacial beds.f 



Again, in the valley of the ^lackenzie river from Great Slave lake to 

 its delta this formation, according to the following description by the 

 same geologist, underlies the drift and was mostly deposited immediately 



* Manual of the Geology of India, 1879, part i, pp. 391-421. Quart. Jour. Geol. Soc, London, 

 vol. xix, 18G3, pp. .■321-354. Compare Am. Jour. Sci., third series, vol. xli, Jan., 1891, p. 48. 

 tGeol. and Nat, Hist. Survey of Canada, An. Rep., new series, vol. i, for 1885, p. 70 C. 



