162 . Explorations in Colorado. [Mareh, 
erably higher altitude than at present. Towards the southwest it 
drops off suddenly into the lower country containing Rios Piedra 
and Pinos. Where the plateau ends, volcanic and sedimentary 
beds of Cretaceous age appear, extending from the Rio Animas — 
eastward to the border of the district. Above the Cretaceous 
beds Nos. 2 and 3 is a series of shales and sandstones about 
three thousand feet in thickness, and containing coal at a num- 
ber of points, of unknown geological age, though the series were 
thought to be possibly parallel with the Trinidad coal-bearing 
strata, and not of Cretaceous age. 
The work was continued to the extension of the La Plata 
Mountains, among which evidences of former glaciers were found. 
In this region also there are evidences of the former existence of 
two very large lakes at the close of the volcanic activity there. 
The work was then connected ‘to the north and northeast with 
that of 1874, and therewith finished. 
The southwestern division, under the direction of W. H. Holmes 
as geologist, worked over an area of about sixty-five hundred 
square miles. The section of stratified rocks exposed extends 
from the lignitic series to the Carboniferous, including about two 
thousand feet of the former, and slight exposures merely of the 
latter. The heaviest seam of coal examined in the lignitic beds is 
twenty-one feet in thickness. In the Cretaceous beds fossils oc- 
curred in ten distinct horizons, which Mr. Holmes expects to be 
able to identify with corresponding ones on the Atlantic slope. 
The section obtained is the most complete and satisfactory made 
in Colorado up to this time. 
The prehistoric remains in the cafions and lowlands of the 
southwest are of great interest. Many cliff houses built in ex- 
traordinary situations, and still in a fine state of preservation, 
were examined. A good collection of pottery, stone implements, 
—the latter including arrow-heads, axes, and ear-ornaments, — 
some pieces of ropes, fragments of matting, water-jars, corn and 
beans, and other articles were exhumed from the débris of a house. 
Many graves were found, and a number of skulls and skeletons 
that may fairly be attributed to the prehistoric inhabitants were 
added to the collection. 4 
The western or Grand River division was under the charge A 
of Henry Gannett, topographer, with A. C. Peale as geologist. 
The region surveyed embraces the country drained by the Un- 
compahgre and Dolores- rivers and their branches, and the work 
extended about thirty miles into Utah, the total area surveyed 
