260 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



position, but are scattered in clusters, and each cluster has 

 created a mountain. Mount Ellen is constituted by a score 

 of individual lava-masses; Mount Pennell and Mount Hillers 

 each by one chief mass, accompanied by several of minor im- 

 portance ; Mount Holmes by two masses ; Mount Ellsworth 

 by a single one, with many dikes and sheets. Each of the 

 mountains is an individual, topographically as well as struct- 

 urally, and together they constitute a group of mountains, 

 not a range. Mr. Gilbert's note-books contain many sketches, 

 by the aid of which he Avill be able to illustrate all the feat- 

 ures of the peculiar types of structure. 



Before commencing the main work of the season, Mr. Gil- 

 bert made an excursion in search of the outlet of Lake Bonne- 

 ville, the great fossil lake of Utah. During an epoch which 

 was probably coincident with the glacial epoch, the broad 

 interior basin of Utah was covered by a great lake, which 

 overflowed its rim, and sent an outlet to the ocean by way 

 of the Columbia River. When the climate became grad- 

 ually warmer and dryer, the evaporation grew greater and 

 the rainfall grew less, until finally the overflow ceased, and 

 the lake began to dry away and shrink within its shores ; to- 

 day only Great Salt Lake and Sevier Lake remain, but high 

 up on the mountain is carved the Bonneville beach, a perma- 

 nent record of the old flood tide. The search for the point 

 of outlet was successful, and it was found at the north end 

 of Cache Valley, a few miles beyond the boundary of Utah, 

 in the territory of Idaho. The bed of the outflowing stream 

 was traced for a number of miles. The beach lines were seen 

 to run quite to the pass through which the channel was cut, 

 but beyond, on the side of the drainage of the Columbia, no 

 trace of them could be seen. 



Of no less interest was the discovery of a recent orographic 

 movement at the western base of the Wahsatch Range. A 

 great fault runs along that base one of the faults by which 

 the mountain was produced. The block of the earth's crust 

 which lies to the westward of the fault-plane was dropped 

 down, and the block which lies to the eastward was lifted up, 

 and from the eastward block subsequent erosion has carved 

 the range. Along this plane of ancient movement there has 

 been a recent movement. The mountain has risen a little 

 higher or the valley-floor has dropped a little lowei*, and this 



