CENOZOIC TIME — QUATERNARY. 955 



course of about 25° to 30°. The narrow lake trends about S. by W., not far from the 

 direction of movement in the ice-sheet over the region. 



Over Manitoba, the following courses of scratches are reported by S. B. Tyrrell : 

 About Lake Manitoba, S. to S. 13° E. ; about Lake Winnipegosis, S. 13° E. to S. 58° W. ; 

 about Swan Lake, west of Winnipegosis, S. 48°-53° W. ; on Red Deer River, S. 68°- 

 78° W. ; Grand Rapids on the Saskatchewan, S. 2°-62° W. ; at Roche-rouge, S. 12° W. ; 

 Cedar Lake, S. 19°-;;9° W. The southward and southeasterly course is evidently due to 

 a valley movement along the lakes. For others, over the interior of North America, see 

 Upham's paper on Lake Agassiz, Can. Geol. Bep. for 1888-1889, and other Reports of the 

 Canada Geological Survey. 



In the use of scratches to determine direction of flow, the directions on page 942 

 should be observed. When sci'atches having different courses occur at the same locality, 

 it is also to be remembered that direction of general movement in the ice-mass depends 

 on the slope of the upx)er surface, as is true for any liquid ; and therefore that the thinning 

 of the ice from melting may change the direction of movement at bottom. But where 

 thinning has diminished the slope of the ice-surface below the angle required for flow, 

 the ice is that only of a dead glacier. 



Bowlders were observed in Northampton and Monroe counties. Pa., by Lewis 

 and Wright, which must have come from the Adirondacks. One of them of " labradorite 

 syenyte," 2\' in diameter, was found in Upper Mount Bethel just south of Kittatinny 

 Mountain; another, similar, measuring 4' x 3' x 3', on the moraine near Taylorsburg, 

 between Kittatinny Mountain and Pocono Mountain ; and another, of gray Adirondack 

 granite, containing magnetite, near Fork's Station, in Paradise, 5 miles north of Pocono 

 summit, at a height of 1550' ; and bowlders of gneiss are abundant over the Pocono 

 plateau, 2000' above sea level. {Geol. Bep. Pa., vol. Z, On the Terminal 3Ioraine in Pa. 

 and N". T., by H. C. Lewis, 1884, with an Appendix on the Terminal Moraine in Ohio and 

 Kentucky, by G. F. Wright.) 



General direction of flow. — From the Laurentide ice-plateau, or that 

 which covered the Canada watershed and extended westward and north- 

 ward, the flow was not only eastward and westward, but also northward, from 

 its northern part toward the Arctic seas ; and along the great eastward bend 

 in the plateau over Canada south of Hudson Bay to Labrador, it was south- 

 westward on the western part, and farther east, southward and southeast- 

 ward. The observed courses of transported stones and lines of abrasion are 

 the means of locating the summit region of the ice-plateau. 



High mountains outside the plateau also influenced the flow, for they are 

 regions of greatest precipitation. The White Mountains, Green Mountains, 

 and Adirondacks, combined into a common plateau by the ice, was one 

 of these mountain regions, apparently determining southeastward directions 

 of movement over New England and southwestward over Pennsylvania and 

 much of iSTew York. In western New York and over the higher parts of 

 Ohio the flow was again east of south ; but beyond Indiana to Dakota the 

 direction was in general southward and southwestward, as if from an ice- 

 plateau in the Lake Superior region. 



But above these plateaus, and farther north, dominated the higher 

 Laurentide ice-plateau, which appears to have been the chief source of 

 movement southward for the region during the time of maximum ice, although 

 there were many subordinate sources. 



