TERRACES WEST OF KELLOGG REGION 529 



at an elevation of probably 300 feet above the river at Rose Lake station, 

 above which the debris is exclusively of Cataldo quartzite. 



West of Eose Lake station granite boulders are scattered along both 

 sides of the valley almost down to the river level. On the north side, a 

 little over a mile west of the station, there is a boulder of granodiorite 5 

 feet long, 4 feet wide, and projecting 3i/^ feet from the ground. About 

 11/^ miles north of Lane there is a granodiorite boulder 6 feet in diam- 

 eter and 3 feet high. The largest granodiorite boulder in Lane is 6 feet 

 long, 5 feet wide, and 3 feet high above the soil. Granite and associated 

 igneous debris are plentiful on the slope back of Lane to a height of 150 

 feet above the river and are sparingly scattered up to a rock bench 

 whose height I estimated at 400 feet above the river. On another rem- 

 nant of the rock bench there is a 30-inch boulder of granite. Several 

 small boulders of basalt are the first representatives of that rock that I 

 have seen in connection with the granite boulders. These rock benches 

 probably represent the 600-foot terrace, being the rim-rock of the deep 

 old channel that at this point probably extends much below the present 

 river 'level. Near Lane station there is a well that penetrates river 

 gravel and yellow sandy silt, such as are found in the bottom of the old 

 valley above Eose Lake. 



Detailed investigation Avas not carried farther down the valley, but I 

 have become acquainted with its general character through railway jour- 

 neys. At Medimont, about 4 miles from Lane, basalt appears in the 

 broad valley at about the river level, and thence to Coeur d'Alene Lake, 

 basalt is frequently seen along the lower slopes of the mountains. In 

 one or two places it seems to form a distinct terrace at about the height 

 of the rock bench at Lane. It is evident that this basalt occurs in the 

 old valley that was excavated and filled to form the 600-foot terrace. 

 Its introduction into the western portion of this valley must have ob- 

 structed the drainage and caused the accumulation of unconsolidated 

 deposits in the valley east of it. The absence of any such accumulation 

 in the reopened valley and the size of the canyon excavated in the lava 

 filling of the western portion of the old valley indicate that the lava 

 probably entered and obstructed the old valley immediately after it had 

 been cut down to its maximum depth. Indeed there can be little doubt 

 that it was the presence of the lava that caused the deep accumulation 

 of fine gravel, sand, and silt in the old valley. The lava barrier rose 

 more rapidly than the river could aggrade its channel and a lake was 

 formed — Lake Latour. This was of an extent and depth comparable 

 with the present Cceur d'Alene Lake. The white and variegated silts 

 (Latour formation) were laid down in it. There is evidence of their 



