200 D. D. CAIRNES SECTION ALONG YUKON-ALASKA BOUNDARY 



ceous matrix, in which are imbedded angular to subangular pebbles and 

 boulders ranging in size from microscopic to 3 or 4 feet in diameter. 

 The matrix appears to have approximately the composition of a boulder- 

 clay, and the greater number of the pebbles and boulders are composed of 

 limestone or dolomite, but some were noted that were composed of other 

 sediments, such as sandstone, conglomerate, and shale. 



The prevailing red color of the matrix is due mainly at least to the 

 considerable amount of iron contained in the matrix, which has in places 

 the general appearance of a hematite ore. The conglomerate, where ex- 

 posed on a small tributary of Tatonduk Elver, is quite unstratified and 

 has the general appearance of a consolidated and iron-stained boulder- 

 clay. The pebbles and boulders are irregularly distributed and are often 

 quite isolated and completely surrounded by the matrix instead of resting 

 on one another, as in the case of a shore conglomerate. 



This conglomerate is thus undoubtedly of terrestrial origin, the term 

 terrestrial being used to imply deposition on the land in contrast to depo- 

 sition in the sea or on the seashore. Land deposits may, however, be 

 formed in numerous ways, mainly by the action of lakes, rivers, winds, 

 glaciers, and volcanoes, as well as by weathering, creepage, or sliding. Of 

 these, considering the thickness of this conglomerate, its unstratified con- 

 dition, and the irregular distribution, composition, angularity, and size of 

 the pebbles and boulders, the only two modes of origin which appear to 

 at all satisfy the field observations are glacial action and creepage or 

 sliding. 



In general composition this conglomerate appears to much more re- 

 semble a boulder-clay than it does slide material, but, on the other hand, 

 its prevailing reddish color and the fact that this conglomerate has not 

 been previously described as occurring in Yukon or Alaska, so far as the 

 writer is aware, and is thus probably not very extensive, would tend to 

 disprove the glacial theory of origin. Also no striated pebbles were 

 found; this may, however, be due to the fact that since the pebbles are 

 dominantly composed of soft materials, such as limestones and dolomites, 

 the scratches, even if they ever existed, might readily have become obliter- 

 ated. Further, due to peculiar circumstances, the writer was able to ex- 

 amine this conglomerate in only one very limited area and could devote 

 but a few hours to the examination ; thus striated pebbles may well occur 

 and not have been found. Pebbles having faceted surfaces, much re- 

 sembling "soled" pebbles, were, however, noted to be somewhat plentiful. 

 Due to its prevailing color, also, this conglomerate could be seen to extend 

 for several miles to the west of the area examined, showing it to be some- 

 what extensive for slide material. This, taken in conjunction with the 



