CENOZOIC TIME — QUATERNARY. 989 



King and Eussell deduced nearly corresponding conditions from tlie region of Lake 

 Lahontan. Tliey describe large depositions of tufa during a warm interval of evapora- 

 tion ; and a second deposition during the final desiccation. The latter produced, besides 

 some tufa, a mineral which became changed to calcium carbonate (thinolite of King, 

 page 133). Lake Mono and other lakes in the Basin experienced similar changes. 



The Great Basin owes its existing dry condition to (1) the feeble amount of annual 

 precipitation (less than 8 inches, according to Schott's chart) and (2) the great evapora- 

 tion caused by the high temperature of the region. The precipitation would have been, 

 even in the Glacial period, relatively small ; but the temperature then was cold, to freez- 

 ing, and consequently evaporation became relatively small. It is thus argued that the 

 lakes of the Great Basin were swollen during the times of Glacial cold, owing to the dimin- 

 ished evaporation and some melting ; that floods from the melting at the time of the 

 Glacial retreat would have added largely to the waters and carried them up to a state of 

 maximum height ; that the waters would have diminished during the following return of 

 glaciers over the neighboring mountains ; and then would have reached a second maximum, 

 when melting again made floods under the warm climate and abundant precipitation of 

 the Champlain period. The floods having passed, a drier climate ensued ; and that is 

 still continued. 



EROSION, TRANSPORTATION, AND DEPOSITION. 



To Champlain history belong the events that occurred during the time of 

 land depression and warm climate of the Middle Quaternary. The work of 

 erosion, begun in the later Tertiary, and carried on over the continent and 

 about the newly lifted mountains and elsewhere by the ice and waters of the 

 Glacial period, was continued with great energy through the earlier part of 

 Champlain time ; and the results are to be seen in the bold and crested 

 heights and deep canons of the Rocky Mountain region, and in deeply cut 

 gorges over a large part of the land. But later in the period, transportation 

 and deposition were the chief work of the rivers. There were also shallow 

 lakes about which Mammals congregated and left their bones in lacustrine 

 deposits. Peat beds and marshes abounded, and these have special interest 

 from the remains of Champlain life which they contain, especially the heavy 

 Herbivores which became mired in them in their efforts to escape from 

 pursuit. Cave deposits also have prominent importance, they having been 

 the resorts of Carnivores, Rodents, and other species, and containing also 

 bones of the various animals dragged in for food. And as the caverns 

 commonly occur in limestone, the deposition of stalagmite over the floor of 

 the cave has often enveloped in stone, skeletons and their fragments, with 

 other relics of the occupants. 



Champlain seashores also have their deposits ; and by means of their 

 numerous shells and other fossils of shallow- water and beach-made accumu- 

 lations, they mark the limits, as already shown, of marine submergence in 

 many regions from which the sea is now excluded. 



Fluvial and lacustrine deposits. — The Champlain subsidence diminished 

 the pitch of southward-flowing rivers. It sometimes redticed it to zero, 

 when lakes formed if there was room for them ; and occasionally it reversed 

 the direction of flow in a stream. Consequently it converted excavating 



