of Milk R. They are at first flat topped plateaus rather than ridges, though they appear as such from a distance. They do not depend on the geological structure of the country but on water erosion acting on horizontal beds. After crossing the St. Mary's however the ridges are steeper & frequently seem to depend on sandstone beds which stick out along their tops.
The folding due to the mountain elevation therefore appears to begin abruptly.

Cannot tell to what formation sandstones seen belong.

The country has been of better character since leaving the Buttes than E. of them, but has now a very fertile appearance. This may be said to begin about the 3rd crossing of Milk R of the line.