88 REPOET UNITED STATES GEOLOGICAL SURVEY. 



were in intimate connection with the glaciers. By the term, I merely 

 wish to designate snch localities that now are perfectly or nearly dry, 

 while in former times tbey contained more or less extensive bodies of 

 water. On the maps heretofore published of that section of country the 

 region is generally described as an " elevated plateau with fresh-water 

 lakes and timber." This view argues against the recent dates usually 

 given on the maps, for no lakes have existed there for a long time, 

 geologically speaking. 



On the higher portions of the plateau none were noticed as having 

 formerly existed. In a number of the stream-valleys, however, there is 

 proof that at one time quite considerable areas were covered with water 

 that to-day show nothing but drift and soil. Near the junction of the 

 two main branches of the Pi-ce-ance there was formerly a lake of about 

 two to three miles in length, tilling the level portion of the valley. 

 Smaller ones were located farther down stream, and are indicated now 

 by the existence of " alkali-Hats." On Douglas's Creek, within the area 

 covered by the Wasatch Group, a few small lakes were along the pres- 

 ent course of the stream. West of it, on Evacuation Creek, about fifteen 

 miles south of White Eiver, there are beds deposited into a lake of 

 about four miles in length and a mile in width, while lower down simi- 

 lar places are found. At the junction of Bittervvater and Sweetwater 

 Creeks another lake originally existed, but has long since dwindled 

 down to a shallow, highly alkaline pond. 



The existence of these former lakes is indicated by several features 

 of unmistakable character. Sometimes (Pi-ce ance) low benches are 

 formed along the bases of the bluffs inclosing the valley. Generally 

 they are removed, however, being composed of very light material. An 

 exceedingly even distribution of fine sand and silt over a level place, 

 which is surrounded, perhaps, on all sides by abrupt bluffs, furnishes 

 another indication. Not unfrequently will it be found that iu such an 

 instance the exit of the stream from the valley takes place through a 

 very narrow opening in the rocks composing the adjoining hills. 

 Swamps, iu perfectly level places, where often the stream itself ceases 

 to be definable as such, and small ponds, sometimes remain to mark the 

 spot where at one time water existed in greater abundance. Alkali, 

 deposited by evaporating water, which accumulates in these places 

 during the wet season, occurs regularly at all favorable localities. 



It seems possible that most of the lakes were formed merely by an 

 accidental stoppage of the river, either through an accumulation of 

 drift-matejial or a blocking of some narrow passage. They probably re- 

 mained for a considerable period of time, which is shown by the enor- 

 mous amount of silt and sand that has been deposited at those locali- 

 ties, and by the perfect levelling of the niveau they once occupied. As 

 a cause tor their disappearance I regard the gradual raising of the lake- 

 bed by the constant transportation of sand and silt into the still water. 

 Thus, of course, the level of the water was raised, the horizontal ex- 

 tent of the lake became greater, while its depth diminished, until at 

 last the sheet of water disappeared entirely, either by flowing oft' or by 

 evaporation. Though occurring quite frequently, the former lakes have 

 water now at but few places. These spots are chosen as favorite resorts 

 by wild water-fowl, and hunting them there is frequently accompanied 

 by great success. 



DRIFT.. 



That species of drift which has been dcwsignated as " avalanchial" is 

 found mainly in White Eiver Caiion. We have, in our district, no 

 mountains of any great height, or occurring iu isolated groups, where 



