THE POPULAR SCIENCE MONTHLY. 



POPULAR MISCELLANY. 



The Old Riyer-Beds cf Middle California. 



— Old river-beds are found in nearly all 

 countries which have been affected by drift 

 agencies. They are also found in Califor- 

 nia, but, while in other parts of that State 

 they present general features similar to those 

 of the Eastern States, those of the aurifer- 

 ous slate belt of middle California are en- 

 tirely different in character and in their sit- 

 uation as respects the present river-beds, and 

 are in some respects unique. In most other 

 countries the present river-beds occupy the 

 same position as the old ; the rivers of mid- 

 dle California have been displaced by lava- 

 flows from their former position, and com- 

 pelled to cut entirely new channels. Instead 

 of cutting these channels at a higher level 

 than the older ones, as has been usually ob- 

 served, the displaced rivers in California 

 have cut them two or three thousand feet 

 deep in the solid slate, leaving the old de- 

 tritus-filled channels far up on the dividing 

 ridges. In other parts of the United States 

 the drainage system has remained substan- 

 tially unchanged since Tertiary times, but 

 in this California region the new drainage 

 system is entirely independent of the old, 

 having the same general direction, but some- 

 times cutting across it. The detritus in the 

 old river-beds of California is composed of 

 large pebbles and bowlders, instead of the 

 silts generally found, and is capped by lava 

 or other volcanic material. In these obser- 

 vations Professor Joseph Le Conte and Pro- 

 fessor Whitney substantially agree. Pro- 

 fessor Le Conte has made a further study 

 of the phenomena, and has given his con- 

 clusions in a paper in the last number of the 

 "American Journal of Science." The old 

 stream-beds, as they are exposed in the 

 processes of hydraulic mining, are shallow, 

 lowest in the middle and rising to the sides, 

 with such forms ground upon the surface 

 of the bed-rock at their bottom as are al- 

 ways produced by swift currents carrying 

 coarse materials, and are in marked contrast 

 with the deep, sharply V-shaped canons 

 which characterize the present rivers in the 

 same region. The filling up of the beds 

 consists of a lower course, sometimes a few 

 feet, sometimes many feet in thickness, of a 

 conglomerate of pebbles and bowlders of 



! considerable size, cemented with sand and a 

 blue clay. Above this are alternate layers 

 of pebbles, gravel, sand, and clay, with frag- 

 ments or trunks of trees of the Pliocene 

 age, and bones of the mammalia of the Pli- 

 ocene and Quaternary ages, and perhaps 

 human relics. Above the detritus is a cap- 

 ping of volcanic matter, a tufaceous con- 

 glomerate, with or without basalt over it. 

 Professor Le Conte accounts for the singu- 

 lar phenomena by a theory, the principal 

 features of which are that the old drainage 

 system began to be formed after the birth 

 of the Sierra Nevada, at the close of the 

 Cretaceous period, and continued to exist 

 through the Tertiary ; the Sierra rose during 

 the Glacial period, accumulated great masses 

 of snow and ice and glaciers that were to 

 play a part in filling the beds, and made the 

 courses of the rivers much steeper than they 

 had been before. The eruptions which threw 

 out the volcanic products were preceded by 

 a period of underground heat which melted 

 the accumulated ice-masses. The waters 

 and ice rushing in violent torrents brought 

 down the coarse gravels and masses of rock, 

 and dropped them as they became too great 

 a load for the streams to carry. Afterward 

 came the eruptions, first of ashes, then of 

 lava, which flooded the mountain-slopes and 

 completely obliterated the drainage system, 

 Coincidcntly there were a considerable eleva- 

 tion of the Sierra range and an increase of 

 the mountain-slope. The glaciers and rivers 

 now began to cut a new system of channels 

 independent of the old ones. They pre- 

 ferred the old divides, for the lava was 

 thinnest or wanting there. As a necessary 

 consequence of the increased elevation, the 

 new chaimels were cut down to a level be- 

 low that of the old ones. 



Age of the Green Mcnntains.— Professor 



James D. Dana gives, in the " American 

 Journal of Science " for March, his reasons 

 for having in the new edition of his " Ge- 

 ology " referred the epoch of the formation 

 of the Green Mountains — in the system of 

 which he includes the whole region between 

 the Connecticut and the Hudson — to the 

 close of the Lower Silurian period. They 

 are, when summarized : 1. That the western 

 half of the region is proved to consist of 

 rocks of the Lower Silurian age, and of one 



