68 
Psyche 
[June 
Undoubtedly the question now arises as to the reason for 
its limitation to White Rocks. Surely this is not due to its de- 
pendence upon the cactus flowers for the same species of plant 
has been found quite generally distributed thruout the West. 
There is but one solution left. It must be dependent upon the 
rocks themselves. And, to be sure, I was able to show that the 
nest of this bee actually was in the sandstone of this locality. 
This seems to indicate that the bee can not make its nest in 
earth but only in sandstone; and being so well isolated from all 
other available rock formation, it of necessity is limited to White 
Rocks. Two facts further strengthen this explanation: First, 
the bee is small and a weak flier — I have not found it beyond a 
radius of fifty yards from the nest. Second, due to the continual 
tillage of the soil, the cactus plants have practically been elim- 
inated from the adjacent territory although they are very abun- 
dant at White Rocks. Thus the bee is apparently limited to 
this environment. 
This remarkable locality has a peculiar history. According 
to Professor R. D. George, head of the geology department of 
the University of Colorado, the White Rocks constitute the so- 
called “Laramie formation. ” This was laid down in fresh water 
lake basins in which, at times, vegetation grew so abundantly 
that extensive deposits were formed. Later, these were changed 
by biochemical and dynamochemical processes to coal. The 
sandstone over the coal was formed by the carrying of sand into 
the lake basin and its later solidification by pressure and an 
added binding material. Following this, the lake disappeared. 
The rock, exposed to the atmosphere, dried, shrank and the 
stresses were relieved by cracks radiating from centers of stress. 
The connections between these joints formed polygonal blocks, 
or “turtle backs.” The joints were deepened by water freezing 
and thawing thereby loosening the sand grains which were later 
carried away by the winds. This process was repeated and in 
time little basins, several feet in width, were formed until now, 
in some cases, the joints are less emphasized. The cliffs, which 
rise to a height of 87 feet, were the banks of the stream which 
had cut out the rock along its broad valley. 
