18 TERTIAKY INSECTS OF NORTH AMERICA. 



surrounding region. To the southeast is Pike's Peak ; to the west South 

 Park and tlie canon of the South Platte, shown by a depression ; to the 

 extreme south the grand canon of the Arkansas ; wliile to tlie north a few 

 sharp, ragged, granite peaks surmount the low wooded hills and ravines 

 characteristic of the nearer region. Among these hills and ravines, and 

 only a little broader than the rest of the latter, lies, to the south, the ancient 

 Florissant Lake l^asin, marked by an irregular L-shaped grassy meadow, 

 the southern half broader and more rolling than the northwestern, the latter 

 more broken and with deeper inlets. 



Recalling its ancient condition it will appear that this elevated lake 

 must have been a beautiful, thougli shallow,' sheet of water. Topaz Butte, 

 and a nameless lower elevation lying eight kilometers to its southwest, 

 which we may call Castello's Mountain, guarded the head of the lake upon 

 one side and the other, rising 300 or 400 meters above its level. It was 

 hemmed in on all sides by nearer granitic hills, whose wooded slopes came 

 to the water's edge ; sometimes, especiall}' on the northern and eastern sides, 

 rising abruptly, at others graduall}" sloping, so that reeds and flags grew 

 in the shallow waters by the shore. The waters of the lake penetrated in 

 deep inlets between the hills, giving it a varied and tortuous outline : 

 although only about 16^ kilometers long and very narrow, its margin must 

 have measured over 70 kilometers in extent. Still greater variety was 

 gained b}'' steep promontories, 20 meters or more in height, which pro- 

 jected abruptly into the lake from either side, nearly dividing it into a 

 chain of three or four unequal and very irregular open ponds, running in 

 a northwest-southeast direction, and a larger and less indented sheet, as 

 large as the others combined, connected with the southwesternmost of the 

 three by a narrow channel, and dotted with numerous long and narrow 

 wooded islets just rising above the surface. 



The ancient outlet of the whole system was probably at the southern 

 extremity; at least the marks of the lake deposits reach within a few meters 

 of the ridge which now separates the waters of the Platte and Arkansas; the 

 nature of the basin itself, and the much more rapid descent of the present 

 surface on the southern side of this divide lead to this conclusion. At the 

 last elevation of the Rocky Mountain chain the drainage flow of this imme- 

 diate region was reversed ; the elevation coming from a southerly or south- 



' The shallowness of the lake is indicated by the character of the fish, the sun cracking of some 

 of the shales and the erect sequoia stumps. 



