T50 UNIVERSITY OF COLORADO STUDIES 



distance into the non-fossiliferous beds, and in other places wells have 

 been sunk, affording excellent sections and showing that the floor 

 deposits extend to considerable depth — just what depth we have not 

 learned. The fossiliferous beds above the floor deposits are approxi- 

 mately twenty feet in thickness. 



The dip of strata is in most places to the northwest, as would be 

 expected in view of the supposed tilting, and is not usually very marked. 

 The beds are not entirely free, however, from local disturbance. In 

 one place we found a very decided change in both direction and angle 

 of dip within a few yards, but the intervening rocks were deeply buried 

 by debris, so we were unable to ascertain whether it was a fault or 

 fold. Near the southern end of the basin the shales seem to be in- 

 volved with igneous rocks, but Hmited time prevented a thorough 

 examination as to the nature of the disturbance. 



Volcanic rocks bordered and projected into the lake in many places. 

 To a layman perhaps the most interesting feature of the igneous rocks 

 is an exposure a few rods north of Florissant post-office. The deposit 

 is much shattered, the cracks varying from a fraction of an inch to 

 several feet in width. It is reported that these crevices afforded hiding- 

 places for the Indians in their wars with neighboring tribes before 

 the advent of white men, and rude fortifications remained there long 

 after the settlement of the valley. 



Since the deposition of the beds and the drainage of the lake, the 

 valley has been subjected to extensive erosion. The fossihferous 

 part of the lake formation, consisting chiefly of soft, yielding shales, 

 has mostly been cut away, leaving remnants, however, along nearly 

 the whole margin, not only of the main shore, but also of the granitic 

 hills which once formed islands in the lake. There is no reason to 

 doubt that at many of the outcrops the top of the formation still remains 

 intact, so that a complete section of the entire formation is obtainable. 

 The exposed shales are usually so badly weathered that the contained 

 fossils cannot be obtained in good condition, but upon steep slopes 

 it is easy to excavate sufficiently with pick and shovel to reach unweath- 

 ered deposits in which may be found fine specimens. The floor deposits 

 are mostly covered by alluvium and talus, and are thus hidden from view. 



