Geology. . 243 
this clay contains scratched pebbles, and overlies coarse gravel at 
a height of 180 feet above the river 
Professor Wright remarks that the area of the part of the Del- 
aware valley that was covered by the ice was not far from 6,000 
about 1,500 feet; and, further, that, with the water at Trenton 
150 feet deep, as the clay-beds would seem to indicate, the 
16 months. He hence concludes that, as this rate of discharge is 
highly improbable, there must have been “a depression of the 
region to the extent of 100 or more feet”; the era in which it 
took place was that of greatest depression during the ag See 
i i ren- 
ura-Trias of Southwestern Colorado; by R. C. Huts. 
(Communicated).—The Jura-Trias period of Southwestern Colo- 
rado is divided into three epochs, not always clearly defined but 
well marked on the Rio De Las Animas, about three miles above 
Animas City, also on the Rio Dolores about 19 miles below Rico. 
The rocks of the lower epoch are exposed on the Uncompahgre, 
San Miguel, Dolores, La Plata, Animas and Florida. They con- 
‘ist of dark brown sandstone and conglomerate and_brick-red 
Sandstone and shale resting comformably upon the purplish beds 
of the Permo-Carboniferous. 
e strata aggregate about 1,000 feet in thickness and are 
Seemingly destitute of fossils. 
The rocks of the middle epoch, absent on the Uncompahgre, 
Which the pebbles are so small, well-rounded and compactly 
cemented as to suggest, at first glance, an odlite. It is character- 
istic of the middle series and generally contains fragments of bone 
and teeth of saurians. : 
+n the light-colored sandstone indistinct leaf impressions are, in 
Some places, quite numerous. Tracks of a diminutive species of 
