May 19, 1921 abstracts: geology 235 



alluded to, there would seem to be no reason for hesitation, unless 

 thorough-going application of the former method should involve an 

 entirely disproportionate number of nomenclatorial changes. 



As evidence on that score it may be said that if 159 out of 193 fam- 

 ily names in a standard work on mammals and 63 out of 71 in another 

 on birds are now based on the oldest genera (and undoubtedly these 

 are fair samples), the percentage of change required to bring all fam- 

 ily names into agreement in this respect is by no means appalling. 

 On the other hand, the search for priority among possible family 

 designations has hardly begun and we know not through what no- 

 menclatorial upheavals pursuit of that policy might lead us. 



ABSTRACTS 



Authors of scientific papers are requested to see that abstracts, preferably prepared 

 and signed by themselves, are forwarded promptly to the editors. The abstracts should 

 conform in length and general style to those appearing in this issue. 



GEOLOGY AND HYDROLOGY.— (7^o/og:^' and ground waters of the western 

 pari of San Diego County, California. Arthur J. Ellis and Charles 

 H. Lee. U. S. Geol. Survey Water-Supply Paper 446. Pp. 321, pis. 47, 

 figs. IS. 1919. 



The report treats of the physiography, geology, and ground-water resources 

 of that part of San Diego County, Calif., which is drained directly into the- 

 Pacific Ocean, and includes a geologic map of this area. This region consists 

 of a mountainous highland area, and a narrow belt along the shore character- 

 ized by broad flat-topped sea terraces. The mountains of the highland area 

 are believed to be due principally to erosion, but differential crustal move- 

 ments have also been largely effective in mountain building. 



Comparatively flat tracts, or "highland basins," some of them surrounded 

 by steep mountain walls, cover many square miles within the highland area. 

 These tracts lie in three belts parallel to the trend of the main drainage divide, 

 and may be remnants of a peneplain, many other remnants of which are 

 preserved as flat-topped mountains. Several faults, presumably of consid- 

 erable magnitude, have been identified, and numerous others are suggested 

 by topographic evidence. 



The drainage pattern shows a tendency for the streams to follow parallel 

 courses and to make rectangular changes of direction. The drainage basins 

 are unsymmetrical. There are places in all the principal valleys where the 

 bed-rock floor is deeply buried beneath detritus, and several of the principal 

 streams, after crossing deep valley fill, flow through narrow rock-bottomed 

 gorges. 



