104 GEOKGE MEKCEE DAWSON ON THE 



the rocks themselves. The pebbles and boulders very generally 

 show a clear relation to the rocks of the country over which they lie, 

 being composed in great part of these rocks, but mingled always 

 with some proportion of foreign material. The surface of the basaltic 

 plateau above described shows, for instance, not only basalt of varied 

 texture in great abundance, but a considerable quantity of fragments 

 from the Lower Cache Creek Series of the Geological-Survey Reports ; 

 some, pretty certainly derived from the Cascade Crystalline Series ; 

 and others, of which it is not always possible to trace the source, 

 but which certainly do not occur on the plateau. "Where those 

 varieties of basalt which easily break on weathering into polygonal 

 fragments occur, the overlying Boulder-clay is filled with them, so 

 that in many places, after prolonged subaerial weathering, the sur- 

 face appears to be absolutely composed of blocks of stone. 



The general direction of movement of the travelled constituents 

 of the Boulder-clay appears to have been southward, though the 

 diversity of the rock formations, and our present ignorance of the 

 details of their distribution, preclude to a great extent, the use of 

 erratics in this inquiry. 



Boulder-clay has been noted in the Cariboo country up to over 

 4500 feet, though the stony materials appear near this elevation to 

 be becoming more angular. The state of the weather during my 

 visit to the region prevented the examination of higher levels. Be- 

 tween Quesnel and Blackwater Bridge it forms an undulating 

 plateau, of which many portions surpass 3000 feet, levelling up the 

 irregularly hilly surface of the hard old rocks below. Between 

 Blackwater Bridge and Port George it appears at all heights up to 

 over 3400 feet. Waterworn transported pebbles are found on the 

 summit of Tsa-whuz Mountain, above mentioned, while on its nor- 

 thern slope a great collection of larger erratics appears. North of 

 the Blackwater, in longitude 124° 30', several broad ridges with ele- 

 vations of from 4000 to 4300 feet are entirely covered with drift- 

 material, with the addition of great numbers of boulders larger than 

 are elsewhere seen. Two high hills passed over by the trail from 

 Fraser to Stuart Lake, with elevations of 3792 and 4910 feet, are 

 covered to the summit with Boulder-clay of the usual appearance, 

 but holding more well-glaciated stones than usual, some of which 

 have evidently been derived from the north. In the Chilcotin country 

 similar deposits overlie the basaltic plateau at elevations above 3000 

 feet. These instances may serve to illustrate the distribution of the 

 Boulder-clay without entering further into details or attempting to 

 describe the numerous localities in which it has been examined. 



In one place only have I found what I believe to be the upward 

 limit of these deposits. This is on the northern slope of the 11-ga- 

 chuz Mountain, at an elevation of 5270 feet, where it coincides with 

 the highest known shore-line. 



In the mixed character of the stones of the Boulder-clay and their 

 very generally rounded and waterworn aspect, though enclosed in 

 material with little or no stratification, the action of water-borne 

 iee, whether iceberg, floe, or shore-ice, seems to be indicated. 



