528 O. H. HERSHEY TERTIARY AXD QUATERNARY GEOLOGY 



low^ with some red, brown, orange, and cream color. In a railway cut 

 about 1^ miles below Cataldo the bulk of the material is an extremely 

 fine silt of white color, though orange, pink, and yellow tints appear in 

 places. It is made up of subangular grains of colorless minerals, chiefly 

 quartz. A silica determination made by Mr. William McM. Huff at 

 Kellogg yielded 93.8 per cent insoluble (presumably silica), the re- 

 mainder chiefly alumina. A bed of white gravel and brown conglom- 

 erate is associated with the silt ; the gravel and silt combined have an 

 exposed thickness of 35 feet and reach a height of 53 feet above the low- 

 water stage of the river. A bed of younger and rather coarse river 

 gravel at the top of the bank forms a terrace whose highest part is about 

 100 feet above the river. Granite and other igneous small boulders and 

 cobbles are scattered on the terrace and extend high on the mountain 

 back of it. 



The old valley seems to run squarely into the present broad valley at 

 Cataldo. Thence for about 2^ miles the valley is a flat-floored basin 

 1 to ]^ miles wide. At the west end the river leaves the broad old 

 valley and enters a newer valley on the south, which it follows to Eose 

 Lake station. The old valley is obstructed by a broad undulating north- 

 south ridge, about 150 feet high, consisting of much fine, well-worn 

 gravel and variegated silts; boulders and cobbles largely of granite and 

 other igneous rocks are scattered sparingly over the higher slopes. iV 

 broad transverse valley on the west of this ridge was cut into the gravel 

 deposit to a depth somewhat below the present river level at Dudley and 

 was subsequently occupied by an arm of Cceur d'Alene Lake. The river 

 built a dike across the south part of the valley, forming a small isolated 

 lake that in time became filled by muck to form the present flat valley 

 floor. On the slope north of the valley there is a granite boulder 6 feet 

 long and 4 feet wide, and near by another boulder 3 feet long. 



Between the extinct lake and Eose Lake the old valley, about a mile 

 wide, is occupied by an undulating country 100 to 200 feet above the 

 river at Eose Lake station. The low ridges consist mostly of old river 

 gravel and sand, some cemented by limonite to brown conglomerate and 

 coarse sandstone; there are also traces of tlie white silts. Cobbles and 

 boulders up to 4= feet in leng-fh, of granite and other igneous rocks are 

 plentifully scattered over the surface of the ridges. On the north border 

 of the valley they are part of a deposit consisting chiefly of angular and 

 subangular local debris, with a number of well-Avorn small boulders of 

 hard dark gray quartzite that are apparently faceted and well scratched 

 as though by glacial action. This deposit forms an imperfect shoulder 



