2a GEOLOGICAL SURVEY OF THE TERRITORIES. 
Scattered around are fragments of a trachyte, which probably caps the 
beds. In one of the valieys Mr. Taggart discovered, ucar an old well, 
pieces of trachyte, which, on looking at the excavation, was found to be 
the first layer penetrated. The point of overflow from which this ma- 
terial came is probably to the southward, in Dr. Endlich’s district. The 
lake basin may possibly be one of a chain of lakes that extended south- 
ward. Ihad thoughtit possible that the beds were of Pliocene age. The 
specimens obtained from bed No. 4, of the section above, were submitted 
to Professor Lesquereux, who informs me that they are ‘Upper Ter- 
tiary.’ ‘But I do not believe, as yet, that the specimens of the Green 
River group, to which your species are referable, authorize the conelu- 
sion of Pliocene age. I rather consider it, as yet, as Upper Miocene. 
The species known of our Upper Tertiary are as yet too few and repre- 
sented in poor specimens tor definitive conclusion. Your specimens 
have a Myrica, a Cassia, fragments of Salix angusta (A. Br.), a Rhus, an 
Ulmus, and a fragment of Poa or Poacites. 
“The shales were so soft and friable that it was rather difficult to 
obtain any Specimens. 
“About one mile south of Florissant, at the base of a small hill of 
sandstone, capped with conglomerate, are 20 or 50 stumps of silicified 
wood. ‘this locality has been called ‘Petrified Stumps’ by the people 
in the vicinity. The specimens of wood are not particularly good.” 
This basin is shown on sheet 13 of the geological atlas of Colorado 
published by Dr. Hayden’s survey, and its outlines are marked with con- 
‘siderable accuracy, although upon a comparatively small scale. The 
data upon which that sheet was constructed have formed the basis of 
the accompanying map, in which the limits of the basin are given with 
closer accuracy and in greater detail.* The point of greatest difference 
is in the valley of Fish Creek, where we noticed no extended prolonga- 
tion of the lacustrine deposits; and as the contours of Dr. Hayden’s par- 
ties themselves seem to forbid the probable extension of the deposits in 
this direction, we have closely limited them to what we saw. 
The ancient lake lies in the valley of the present South Fork of Twin 
Creek, and of the upper half of the main stream of the same after the 
South Fork has joined it. Following the road from South Park to Colo- 
rado Springs, and leaving it just above Florissant Post Office,t and then 
taking the track—half road, halt trail—which leads over the divide 
toward Cafion City, we shall pass between the Platte River and the 
Arkansas divide, through the entire length of the basin. This road 
crosses the South Platte a short distance, say a kilometer and a half, 
below the mouth of Twin Creek, climbs a long, gradual slope on the east 
bank of the river to an open, grassy glade, about 2,500 meters above the 
sea, and then descends a little more than three kilometers from the river 
to join the valley of Twin Creek. We scarcely begin the descent betore 
our attention is attracied by the outcropping of drab-colored shales, which 
continue until almost the very summit of the divide is reached and the 
descent toward the Arkansas begun, a traveling distance of not far from _ 
thirteen kilometers. 
By climbing a neighboring peak, thrice baptized as Crystal Mountain, 
Topaz Butte, and Cheops Pyramid, we obtain an admirable bird’s-eye 
view of the ancient lake and the surrounding region. To the southeast 
* The heights are given in feet. 
+ Florissant is merely a post-office at Castello’s Ranch, which is also provided with 
a store, the basis of supplies for all the inhabitants within a radius of fifteen kilome- 
ters. One would have to look tar to find in Colorado a more comfortable hostelry than 
that to which ‘‘Judge” Castello will welcome us. 
