J. LeConte—Old River-beds of California. 179 
bed-rock and the amount of wear, it is certain that the softening 
has taken place since the filling. The surface-forms of the bed- 
rents carrying coarse materials—precisely such as are now pro- 
Sailor’s flat, beneath the volcanic cap, to be presently described, 
logs of Redwood (Sequoia) or of cedar (Libocedrus) probabl 
the latter, in which the bark was still tough and fibrous althoug 
the wood was soft and could be cut like cheese. In the finely 
stratified sands and clays are found beautiful impressions of 
leaves of many kinds. ‘According to Lesquereux these leaves 
Indicate a Pliocene age for the deposits. More rarely mamma- 
lan bones have been found. Among these are allies of the 
thinoceros, hippopotamus and camel, indicating, like the leaves 
a Pliocene age, but also in many undoubted cases the mam- 
* Iti igi idity of this erosion. In the North 
rat achy ee = petharsl he ban toe Be eight months per year, has 
cut in four years a channel three feet wide and fifty feet deep in solid slate. 
