STUDIES FOR STUDENTS 175 



ice. 1 These breccias are very irregular in their distribution and 

 vary rapidly and greatly in their thickness. The fragments are of 

 Cambrian limestone and of the lower limestones of the Quebec 

 group. "The only means of explaining these conglomerates seems 

 to be the action of coast ice ... . which seems to have had great 

 reefs of limestone, probably in the area of the Gulf of St. Lawrence, 

 to act upon and to remove in large slabs and bowlders, piling these 

 up on banks to constitute masses of conglomerate." Walcott also 

 postulates floating ice in the absence of any other explanation in 

 accounting for bowlders in certain intraformational conglomerates, 

 saying: "No other explanation occurs to me that will account for 

 the transportation of a bowlder from the shore line and the placing 

 of it upon the sea-bed so as not to disturb to any marked degree 

 the sediments then accumulating." 2 



The bowlder beds of the Talchir group of India are attributed 

 to ice rafts by Oldham. 3 Sporadic bowlders from distant sources 

 and reaching a maximum diameter of 15 feet are distributed with 

 extreme irregularity in distinctly stratified shales and sandstones. 

 Large numbers occur within limited tracts, but over many square 

 miles of the area they are quite absent. Where the sedimentary 

 matrix is laminated, the laminae bend down beneath and arch 

 over the included blocks. As the fragments are far too abundant 

 and widespread to have been carried by rafts of vegetation, floating 

 ice remains the only possible vehicle. This inference is confirmed 

 by the presence in two localities of striated pebbles, although most 

 of the fragments are distinctly water-worn. The various phe- 

 nomena of the Talchir beds point to their accumulation in large 

 inland water bodies covered with ice in winter, to which torrential 

 streams led down steep valleys and to which glaciers locally 

 descended. 



Tree-raft breccia. — Uprooted trees, drifted down to sea on river- 

 floods, may carry for some distance out from shore angular stones 



1 Sir J. W. Dawson, "On the Eozoic and Paleozoic Rocks of the Atlantic Coast 

 of Canada," Quar. Jour. Geol. Soc. London, XLIV (1888), 809-910, quoting an earlier 

 paper. 



2 C. D. Walcott, "Intraformational Conglomerates," Bull. Geol. Soc. Am., V, 197. 



3 R. D. Oldham, Geology of India, 2d ed., pp. 157-60. 



