/ 
Geology and Mineralogy. 151 
about the lake-area, which want of horizontality in the terraces 
evinces, and the orographic movements that occasioned it ; and 
the region. Mr. Gilbert observes that the highest water-line 
about Lake Bonneville (the flooded Great Salt Lake and other 
Utah lakes combined) is 1000 feet above the level of Great Salt 
Lake; and “over every fvot of the intervening profile can be 
traced evidence of the action of waves.” This 1000-foot terrace 
is called the Bonneville shore-line; and another, which is espe- 
cially conspicuous, at a level of 400 feet, is called t 
The remarkable terraced features of the region, 
shore-line, 
rid 
being about 100 feet below those at intermediate points (at 
les. 
Mr. Gilbert deduces from the observations that an increase in 
elevation of the Wasatch Mountains may be still in progress. 
ne 
latest movement is indicated y the character of the erosion ; 
that the eroded slopes are not a result of subaerial action, _ 
. 
are characterized by the peculiar sculpture of waves; that the 
vos 
Salt Lake have not since been even 50 feet higher than they are 
at present. He adds that this uplift is therefore so recent ‘as to 
leave no reasonable suspicion that its growth has now ceased.” 
€ memoir closes with the following “ summary :” 
(1) The climatic episode of which Lake Bonneville was the 
expression consisted of two humid maxima, separated by an in- 
terval of extreme aridity. The second maximum was the more 
Pronounced ; the first the longer. ‘ 
~ time elapsed since the close of the Bonneville epoch 
has been briefer than the epoch; and the two together are incom- 
parably briefer than such a geologic period as the Tertiary. 9 
3) ‘The period of voleanie activity in the Great Basin, which 
Bonneville Epoch, and presumably have not yet ceased. 
(5) The Wasatch Range, the greatest mountain mass of Utah, 
has recently increased in Ftaht, and presumably is still growing. 
© 
