GEOLOGICAL SUEVEY OF THE TEERITOEIES. 



29 



are some moderately high basaltic ridges, the highest portion of whicli 

 has received the name of Kettletop Butte. Market Lake is a kind of 

 sink, probably produced by the spring overflow of Snake Eiver, and is 

 entirely dry the greater portion of the year. 



On the morning of June 26, 1 started eastward from Market Station 

 toward the Mittes, near the bend of Snake River. The road wound along 

 low basaltic hills, which really form a marked feature over a large portion 

 of this basin. At the present time the surface is perfectly dry, but at 

 some period in the past little streams circulated all over the surface. 



Fig. 3. 



BASALT TABLES, SNAKE RIVER BASIN. 



wearing out their valleys through 

 the basaltic crust, leaving portions 

 like broad table-tops, (Fig. 3,) occu- 

 pying a greater or less area. From 

 beneath these fragments of the 

 crust, the loose sands have been 

 washed out all around, so that the 

 overlai^ping edges have fallen 

 down in every directiou, from a 

 common center in many instances. 



It would appear that these hills show that there were several periods 

 of overflow of basalt, that beneath the sand is another floor, and upon 

 this was deposited at the bottom of a lake a thickness of several feet 

 of sand before the upper floor of basalt was formed. The northern por- 

 tion of the basin is covered with thick beds of sand, into which the 

 wheels of our wagons would sink 2 or 3 feet at times. On Camas Creek 

 are some interesting sand dunes. On the northeast side are some 

 conspicuous hills of blown sand, visible at a distance of twenty to forty 

 miles, which indicate that the direction of the winds is from the south- 

 west. Dry Creek, which in the spring season affords a channel for a large 

 body of water, forms a caiion in the basaltic floor, with walls 50 feet 

 high. In midsummer there is no running water. On this creek there 

 is a stage-station called " Hole in the Wall," which derives its name 

 from a remarkable cave in the basaltic rocks. About a mile west o-f the 

 station there is a depression in the level plain 30 by 50 feet, where the 

 rocks seem to have sunk, revealing on the north side quite a large 

 opening. This opening or cave connects with others to an indefinite 

 extent, under the great basalt floor. We examined several of these 

 caves, which were connected together only by small openings in 

 the partition walls, each with dimensions of 100 to 200 feet in width 

 and length, and 30 to 50 feet deep. The bottoms of the caverns show un- 

 mistakable evidence of having once formed a river-bed. The water still 

 flows at times along the channel. Some person had dug a hole about 10 

 feet deep, which showed the layers of deposition of sand and clay as per- 

 fectly as along the banks of any of our little streams. We see by this 

 illustration (Fig. 4) that underneath this basaltic crust streams of water 



Fig. 4. 



BASALT FLOOR, U NT5 ERLAID WITH PLIOCENE BElaS. 



have worn in the past, and may be now, wearing out their channels toward 

 Snake Eiver, and that this may be only one of numerous examples in this 



