. floods ; nor can we tell how low was the stage 
: Water rose toits last maximum. 
a basin was filled by the melting of glaciers. 
= of Lake Bonneville, Mr. Gilbert seems to 
twas fresh or salt, the evidence derived from 
7 the beds themselves being vague. The $ 
ASS dt, ie Es Deana Oe Py hac SEG eR Ne 5 a OE ne RS id De dee Sa ee 
-Jip aaia 
1876.] The Great Salt Lake in Former Times. 679 
but Iam not aware at what point, nor at what altitude. The 
northern portion of the lake area falls within the fields of study 
of the corps of Mr. King and Dr. Hayden, and when their ob- 
servations and those of Professor Marsh shall have been pub- 
lished, the relation of the beaches to the outlet or outlets will 
doubtless be known. Meantime I anticipate that the Provo 
beach, as well as the Bonneville, will be found to have been de- 
termined by an overflow. 
“ The largest open body lay over the Great Salt Lake Desert, 
and had a depth of about nine hundred feet. The average 
depth of the whole was not far from four hundred feet, and the 
extreme depth one thousand feet. Its area was not far from 
eighteen thousand square miles, being a trifle less than that of 
Lake Huron, and eight times as great as Great Salt, Utah, and 
Sevier lakes combined. Its extreme length, from north to south, 
was about three hundred and fifty miles, and its width one hun- 
dred and twenty-five miles.” 
Mr. Gilbert then describes the beds containing shells deposited 
by this ancient lake, and discusses the question whether the lake 
was originally fresh or brackish. The deposits formed by the 
lake “are largely composed of fine, friable, white calcareous 
marl, and this passes, on the one hand, into a cream-colored, 
partly odlitic sand, of calcareous and silicious grains, feebly ce- 
mented by calcite, and, on the other, into an impalpable clay 
charged with chloride of sodium and other soluble salts. All of 
these beds, excepting the most saline of the clays, are fossilifer- 
a affording, in great abundance, a few species of lacustrine 
gasteropoda.” The area covered by these beds is completely cir- 
cumscribed by the Bonneville beach. “Of the history of the 
h, or, what is the same thing, of the history of the lake, we 
now only the last few pages. We know that the present low 
tide has been preceded by a high tide, the duration of which, 
though extended, was not unlimited, and we know that for a 
comparatively long antecedent period there had been no similar 
; but we do not know that there were or were not earlier 
| from which the 
» The author thinks that the lake 
As regards the water 
be in doubt whether 
both the fossils and 
hells contained in the 
he thinks, may have been borne into the lake by streams, 
