508 



SCIENCE 



[N. S. Vol. XXV. No. 639 



rooted, and now needs only to be judiciously 

 tended and watered. — Boston Evening Trans- 

 crvpt. 



CURRENT NOTES ON LAND FORMS 



DRAINAGE CHANGES IN CALIFORNIA 



J. C. Brannek describes 'A Drainage Pe- 

 culiarity of the Santa Clara Valley [Cal.] 

 affecting Fresh-water Faunas ' {Journ. Geol., 

 XV., 1907, 1-10), in essence as follows: A 

 stream flows westward from the Mt. Hamilton 

 group into the middle of the longitudinal 

 (N.W.-S.E.) Santa Clara Valley of the Coast 

 range, and there builds up a great alluvial fan 

 which forms a divide on the valley floor. The 

 stream at present flows northwest from the fan 

 by Coyote Creek to the southern end of the 

 Bay of San Francisco. Another creek heads 

 in the longitudinal valley near the fan and 

 flows southeast to join Pajaro Eiver, which 

 rims westward into the Bay of Monterey. A 

 slight radial shifting of the stream on the 

 fan would transfer it to the Pajaro system. 

 There is good evidence that such shifting has 

 occurred in the past, probably repeatedly, so 

 that the waters from Mt. Hamilton have 

 found their way alternately into the two bays. 

 Such stream changes would permit a mingling 

 of the faunas of the Coyote and Pajaro basins. 

 Should a long time then elapse without fur- 

 ther changes in drainage, the unifled faunas 

 might spontaneously and gradually diverge. 

 At present the fishes of the two rivers are re- 

 markably alike in most respects; some points 

 of difference are taken to indicate the begin- 

 ning of spontaneous divergence. 



It appears, however, that the faunal pe- 

 culiarities common to these two rivers are 

 noted also in other rivers flowing into the two 

 bays. As the mouths of the rivers are now 

 separated by salt water and as their heads are 

 far apart, a second hypothesis must be ad- 

 vanced to account for the community of forms, 

 which Branner believes to require direct fresh- 

 water connection at some former time. A 

 former elevation of the coast, permitting the 

 rivers of each bay to unite in a main river 

 system, is believed to afford a satisfactory 

 explanation for the phenomena observed. 



Each of the two main river systems would 

 then have had its own fauna, until changes 

 on the alluvial fan, as above described, had 

 mingled them in a single fauna common to- 

 both basins. Submergence would then dis- 

 member or betrunk the two systems, yet the 

 isolated rivers would still have similar faunas. 

 Independent evidence is given of the eleva- 

 tion and submergence here postulated. The 

 amount of elevation is believed to have been 

 great. In view of this it would be interest- 

 ing to know whether the possibility has been 

 considered that, during such uplift, the twa 

 main river systems might have united in one, 

 permitting a mingling of faunas independent 

 of the stream changes on the fan at the divide, 



D. W. J. 



THE PENEPLAIN OP BRITTANY 



E. DE Martonne, lately professor of geog- 

 raphy in the University of Eennes and now 

 in that of Lyons, gives an effective descrip- 

 tion of the peninsula of Brittany, illustrated 

 with expressive block diagrams and photo- 

 plates (' La peneplaine et les cotes bretonnes,' 

 Ann. de Qeogr., XV., 1906, 213-236, 299-328). 

 Brittany is a district of greatly deformed an- 

 cient rocks, worn down for the most part to a 

 peneplain, but retaining here and there cer- 

 tain residual reliefs of moderate altitude; the 

 whole gently up-warped in Tertiary time, and 

 now more or less dissected in a second cycle 

 of erosion. The chief residual reliefs or 

 linear monadnocks follow the east-west struc- 

 tural trend somewhat north of the middle of 

 the peninsula. In spite of their moderate 

 altitude (250 meters), they are sparsely in- 

 habited; some of the peasants there are still 

 ignorant of the French language and speak 

 only Breton. The peneplain, admirably de- 

 veloped and preserved north of the residual 

 hills, is sharply dissected by young valleys 

 towards the bold coast; but when the valleys 

 are followed southward towards their heads 

 they open out on the upland. The peneplain 

 on the southern side of the peninsula is more 

 destroyed by revived erosion, because larger 

 areas are here occupied by relatively weak 

 rocks, some of which have been almost re- 



