160 C. F. TOLMAN 
1890, who found that the remains at that time were of mullet. From other 
sources it seems fairly probable that nearly every flood brings with it shoals of 
fish which find their way into the laguna. The shallow sheet coming in over the 
plain to the southward must furnish abundant food: but as the water rises in 
temperature and increases in concentration, it seems quite probable that a point 
is reached at which the water becomes poisonous to all of the finny inhabitants. 
Furthermore, this condition ensues at once and with sweeping effect, for the dead 
fish go ashore during so brief a period that no marked change of level has taken 
place; and as evaporation may be as great as half an inch a day, and scarcely 
ever is less than a quarter, the disaster must take place within a week or two.? 
Plant remains.—There is a decided dearth of fossil remains on 
both bajada and playa deposits. In regard to the former this is to 
be expected, due to complete oxidation and lack of exploration. The 
playa deposits, especially the fresh-water playas, and the cienegas 
of the semi-bolsons would be expected to contain more in spite of 
subaerial exposure, for wood decay is extremely slow in arid regions, 
and the dense clay ought to help preserve the more resistant portions 
of the plants, such as the sahuaro ribs and such hard woods as mes- 
quite. The prompt decay of the mesquite wood which was immersed 
under the expanded Salton Sea, and now exposed, suggests that even 
a small amount of salt dissolved hastens decay, for the Salton water 
contained (June, 1907, about 25 vears after the first break of the 
river into the basin only) about four times as much salt as the Colorado 
River at low water, and even now it is possible to drink the water 
under stress of necessity.? An interesting problem demands solution 
as to whether or not the Tertiary deserts were more deficient in plant 
covering than those of today. 
Erosion of the dried playa.—This is entirely by wind action. The 
smaller the playa the more likelihood of desert pavements, on account 
of the larger proportion of pebbles contributed by the floods from 
above. Such fossil wind-erosion surfaces have been noted in deposits 
examined. 
Relative importance of lake and outwash deposits.—A brief recon- 
naissance in the Salton Basin gave a good chance to compare the 
relative importance of the lake deposits, and those laid down in the 
bajadas. This basin has suffered many invasions by the river water, 
« MacDougal, “The Desert Basins of the Colorado River,” cited above, pp. 16, 17. 
2 For analyses, see MacDougal, op. cit., p. 3. 
