G. K. Gilbert—Post- Glacial Joints. 25 
bracing only a short period of time when it was thought that a 
longer series of observations would cause the anomalies to dis- 
appear. If any person whose attention is attracted to this map 
should discover in it serious defects, he is urgently solicited to 
communicate to me the observations which indicate these de- 
fects. In my next paper I propose to publish all additional 
observations of rain-fall which I may be able to obtain ; and if 
the present map should be found greatly in error, I intend to 
issue a revised edition of it. 
Art. Il.—Post-Glacial Joints ; by G. K. GILBERT. 
THE following communication is based upon observations 
made by the writer as a member of the United States Geo- 
logical Survey. 
e Sevier Desert lies in Utah, immediately south of the 
Great Salt Lake Desert. Each is a flat, white plain, sur- 
ments—clays and marls—which now constitute the floors of the 
deserts, When the climate changed at the close of the Gla- 
cial Epoch the water gradually dried away, and as it fell there 
came a time when the bottom of the deepest strait was laid 
bare and the lake was divided into two—the representatives 
respectively of Great Salt Lake and Sevier Lake. Their sepa- 
ration was not, however, at first complete, for Great Salt Lake 
fell the more rapidly, and there was a transition epoch during 
which Sevier Lake overflowed to Great Salt Lake. A channel 
of outflow was eroded in the lake sediments, cutting them to a 
depth of more than one hundred feet; and this channel is 
Plainly to be traced at the present time. Indeed it is so con- 
pea a topographic feature that it has been named by trav- 
elérs the “Old River Bed,” and a stage station on the old 
overland road was called “ River-bed Station.” 
One day last summer I stood on a rocky butte which springs 
from the Salt Lake Desert at its southern margin just at the 
brink of the Old River Bed. Behind me at the south there 
were other rocky buttes, and beyond them mountains; and 
