240 University of Kansas Geological Survey. 
often contain in large quantities. Nodular concretions of pyrite are 
found in some localities in great abundance. Near Castle Rock, I re- 
member seeing one such locality years ago, where the small round 
nodules, like grape shot, could have been gathered up by the wagon 
load. The decomposition of these nodules in the chalk produces an 
abundance of gypsum crystals, sometimes appearing on the surface 
as excellent selenite, but more often loosening the chalk into a 
friable dusty mass, injuring or destroying fossils that may be con- 
tained init. Water percolating these.shales becomes so thoroughly 
saturated with styptic salts as to be undrinkable. 
Weathering has left the exposed chalk in many places eroded into 
picturesque objects. ‘The famous Castle Rock, in the valley of the 
Hackberry about ten miles from its mouth is a lone pyramid several 
hundred yards from the upland. My first knowledge of the Rock 
dates from October 1874, and since that time I have seen but little 
evidence of erosion. In various places throughout the chalk beds 
of the Smoky Hill river I have observed marks scratched by myself 
eighteen years previously that appeared as clear almost as when 
they were made. The erosion in general is not nearly so rapid as 
one would think. The smooth, worn surfaces made on the project- 
ing angles of many low cliffs by the buffaloes are still to be seen 
nearly as smooth as they were twenty years ago. Ihave seen build- 
ings made of the chalk more than twenty years ago still remaining 
with but little indications of wear. One such building is at Man- 
hattan, or was a year or two ago, erected by the Union Pacific Raii- 
road company from blocks that had previously done like service in 
western Kansas. Its surfaces show but little effects of weathering. 
rrosion takes place much more rapidly by undermining than by 
direct abrasion of the surface. Blocks lying in their natural plane 
of stratification will strongly resist wear, but when once toppled 
over so as to bring the lines of stratification vertically or obliquely 
they go to pieces within a year or two. 
One of the most famous landmarks of the Niobrara is the Monu- 
ment Rocks on the Smoky Hill river. See Plate XXXVI. When 
I first saw them in 1874 the place had been recently abandoned as 
the stage station of the Overland stage route. A vertical crack in 
the main rock has deepened very much since that time and it is now 
