EXPEDITIOX TO DAVIS STItAIT AND BAFFIN BAY 73 



juents due to <iratlieiit forces and not to tides. The liydrographic 

 charts issued by the United States Xavy show currents of 5 knots in 

 both directions throuoh Hudson Strait, The coarseness of the sedi- 

 ments demonstrates that these currents extend with significant velo- 

 city to the bottom of the Strait. 



Sinuhirh^ the dynamic topographic map indicates a relatively slow 

 movement of water over the well-sorted fine-grained sands northeast 

 of Cape Murchison. Weeks ^ rei:>orts a tide of 25 to 35 feet in Cum- 

 berland Bay which lies northwest of this area. A tide of such 

 dimensions necessitates a considerable forward and backward move- 

 ment of water. As the sediments east of Cape Murchison are in the 

 l)ath of such oscillations, in water only 200 meters deep, it is evident 

 they should be coarse. 



Rock fragments. — The occurrence of gneiss, quartzite, and granitic 

 rocks in the sediments is easily explainable, as the geologic maps and 

 reports of Greenland, Baffin Land, and northern Labrador ^ clemon- 

 strate the prevalence of pre-Cambrian metamorphic and granitic 

 rocks throughout this area. Basalt occurs on Disko Island, which 

 if not the source of the occasional basalt fragments, at least indicates 

 the presence of basic eruptives in the general region. Kindle ^ men- 

 tions the occurrence of Pleistocene shells in the lower part of the ice 

 cap in west Greenland in latitude 74°. The eroded Pelecypod shell 

 in sample 24 may have such an origin. 



HoAvever, the Avidespreacl distribution of noncrystalline limestone 

 is not so readily explainable. The land on both sides of Davis Strait, 

 in the region from which the sediments come, is mapped as consist- 

 ing almost entirely of pre-Cambrian formations. Crystalline lime- 

 stones are plentiful in certain i^arts of the pre-Cambrian, but the 

 noncrystalline aphanitic character of the limestone fragments in the 

 deposits indicates they originated elsewhere. Excluding the sedi- 

 ments east of Cape Slurchison, limestone occurs in almost every 

 sample, and is the dominant rock type in most of the deposits. 



Source of limestone. — The ubiquitousness of the limestone and its 

 plentifulness in the deposits indicates that a very significant propor- 

 tion of the rock fragments carried by the ice consists of limestone. 

 The question is from Avhere did the limestone come. 



Drift ice on the Avest side of DaA^is Strait is estimated by Smith ^^ 

 as consisting of less than 2 per cent berg ice and more than 98 per 

 cent pack ice. Shelf ice, extending from the shore seaAvard; the ice 

 foot, that part of the shelf ice attached to the sea bottom ; and anchor 

 ice, originating on the sea bottom near shore, haA^e opportunity both 



^ L. J. AA'eeks, Cumberland Sound Area, Baffin Land, Can. Geol. Surv. Sum. Rep., 

 1927 C, p. 86, 1928. 



8 Robert Bell, Report of Exploration of Hudson Strait Region, Can. Geol. Sur. Sum. Rep 

 1897 (Ann. Rep. 10) A. pp. 75-83, 1898. 



Geologic Map of North America, U. S. Geol. Surv, 1911. 



O. B. Boggild. The Geology of Greenland, Greenland, Publ. Com. Dir. Geol. and Geog. 

 Investigations in Greenland, C. A. Reitzel, Copenhagen, pp. 185-231, 1928. 



L. J. Weeks, op. cit., pp. 84-95. 



Lauge Koch, Stratigraphy of Greenland, Dissertation for Doctorate, published by 

 Levin and Alunksgaard, Copenhagen. 1929 (contains good bibliograi>hy). 



Geological Map of World, Preus. Landesanstalt, Berlin. 1930. 



» E. M. Kindle. Ice Borne Sediments in Canadian and Other Arctic Waters. Am. J. S. 

 v. 7. p. 277, 1924. 



" Edward H. Smith, Arctic Ice, etc., pt. 3 of Bulletin 19, p. 190. 



68165—32 6 



