20 
GEOLOGICAL REPORT-TBIRTY-FIF$H PARALLEL. 
found mingled with sand, varying from the size of a nut to that of one’s fist, and all were much 
rounded and water-worn. 
This deposite is from one to one and a half feet thick. The recurrence of a similar deposite 
between Camps 26 and 27 is mentioned. Again, near Camp 31, pebbles of quartz, carbonate 
of lime, silex, jasper, gneiss, and rolled fragments of ostrea, were found, which appeared to 
have come from the valley of the Washita. By far the most important deposite of this character 
recorded was found half way between Camps 33 and 34 ; it is t<r very thick, and is formed of 
large pebbles of quartz and granite the size of a gourd ; there is also white sand often fifteen 
feet thick, and very hard.” Numerous little hills of “ diluvium” are mentioned under the 
same date. Similar deposites of pebbles were found the next day above the Canadian river, 
while near it, only white and red sand, without pebbles, was seen. Deposites of this character 
were found along the whole route, and their resemblance to the “ drift,” mentioned by Dr. 
Shumard and others in their reports and journals, will be subsequently noted. 
III. ANTELOPE HILLS TO THE EASTERN BASE OF THE SANTA EE AND SANDIA MOUNTAINS. 
The Antelope hills, sometimes called the Boundary mounds, or Antelope buttes, are well 
known land-marks to the traveller of the valley of the Canadian. The first description of them, 
which I find, is given by Lieutenant J. W. Abert, who states, “ that there are five of them, two 
of which appear perfectly conical, and the group forms one of the most noted land-marks in the 
whole country.” Descriptions of them are given by both Captain Marcy and Lieutenant Simp¬ 
son, who passed up the Canadian in 1849. Lieutenant Simpson 1 observes: “Their height, 
probably from 120 to 150 feet above the plain below, has caused them to be seen for the past 
two days, they having constantly appeared as if they were near at hand ; and yet, when first 
seen, their distance off was under-estimated by some eight or ten miles. Their form is quite 
regular, four appearing, in the distance, of an oblong shape ; the two others conical, and each 
of them capped by a well defined terrace, or rather table, of white vesicular sandstone, eighteen 
feet thick and horizontally stratified.” Captain Marcy 2 also reports them as 150 feet high, and 
states that they are of porous sandstone. “ They rise almost perpendicularly from the smooth 
prairie, are flat upon the top, and present every indication of having been raised out of the 
earth by volcanic agency.” 
The annexed outline sketch, which I have Reduced frorp. one by Mr. Mollhausen, will at once 
convey an idea of their appearance, and show their origin to the geologist. 
They are evidently of horizontal strata, which were once continuous, and which formed a 
plateau raised above the general level of the prairie, butj which, owing to the denudation or 
wearing away by rain-water and streams, has been cut by ravines, and separated into many 
portions, which now constitute the flat-topped mounds. 
Mr. Marcou found that the sandstone of these mounds was friable and of a dirty-white color. 
It is incrusted with carbonate of lime,> and some of the upper beds are entirely of white lime- 
1 Report of a survey on the Upper Arkansas, and the country of the Comanche Indians, 1845, p. 67. 
5 Report of the route from Fort Smith to Santa Fd, p. 180. 
