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The central portion of the old pre-glacial valley is 

 floored with silts and boulder clays, and through these 

 the Lewes has cut the narrow, winding, secondary valley, 

 about 200 feet (61 m.) in width, in which it now flows. 



The oldest rocks known in the district are limestones, 

 which are referred to the Carboniferous. These have been 

 broken through and largely destroyed by three distinct 

 igneous invasions. The earliest invasion was by andesites 

 of various kinds. These were intruded, partly at least, in 

 the form of sheets or sills up to 1,000 feet (304 m.) or more 

 in thickness. The second invasion is represented by 

 plutonic rocks, which range in mineralogical composition 

 from hornblende granites to augite syenites, diorites, 

 and even to gabbros. These rocks cover a large portion 

 of the district and may represent an outlier of the Coast 

 Range batholith. The third period of igneous activity 

 resulted in the production of the numerous porphyrite 

 dikes now found cutting indiscriminately across lime- 

 stones, granites, and older andesites. These dikes occur 

 throughout the district, and in certain areas cover approx- 

 imately half the surface. The youngest consolidated 

 rocks in the district are basalts. These originated outside 

 this belt and entered it through a depression north of 

 Golden Horn. They flowed down the valley of Hoodoo 

 creek to Lewes river, and continued down the river valley 

 to Whitehorse rapids. The basalts were followed by the 

 deposits of the glacial period, consisting mainly of boulder 

 clays and silts, vast quantities of which floor the old valley 

 of Lewes river in the vicinity of Whitehorse. Recent 

 superficial deposits constitute a thin covering overlying 

 the older formations in most places. 



The copper belt, as determined by recent discoveries, 

 extends along the valley of Lewes river, from a point east 

 of Dugdale on the White Pass and Yukon railway, 

 northwestward to the base of Mount Haeckel, a distance 

 of about 12 miles (19-2 km.) The width of the belt 

 seldom exceeds a mile (1 -6 km.), and in places is confined 

 to a single line. The distribution of the discoveries 

 along the belt is exceedingly irregular. The ore deposits 

 are considered to be of contact-metamorphic origin, and 

 their outcrops dominantly follow a series of limestone 

 areas enclosed in granite, but in places occur between 

 granite and andesite. Where the limestone is absent the 

 belt is practically barren; and considerable stretches of it 



