Maech 14, 1902.] 



SCIENCE. 



415 



same drainage basin and followed approxi- 

 mately the same course as the inodern 

 stream. The most western point where the 

 gravels of the Neocene Tuolumne have been 

 preserved is east of the head of Big Hum- 

 bug Creek in the Sonora quadrangle, and 

 the most eastern Piute Canyon in the 

 Yosemite quadrangle. If we now calculate 

 the average grade of the Tertiary stream 

 between these two points, and the average 

 grade of the present river between the same 

 points, we can compare the grades of the 

 two streams. The altitude of the Neocene 

 Tuolumne gravels at Big Humbug Creek is 

 about 2,800 feet, and at Piute Canyon 7,500 

 feet, giving a difference of 4,700 feet. The 

 altitude of the present Tuolumne north of 

 Big Humbug Creek is 1,500 feet, and at 

 Pate Valley, at the mouth of Piute Creek, 

 4,550 feet, giving a difference of 3,050 feet. 

 The horizontal distance between the two 

 points is about 33 miles. Assuming that 

 both the Neocene and the present streams 

 took a direct course, we have a grade of 

 142 feet to the mile for the Neocene chan- 

 nel, and a grade of 92 feet to the mile for 

 the present channel. "Wliile the Neocene 

 river occupied a rugged canyon, neverthe- 

 less this canyon was much less deep and 

 rugged than that of the present Tuolumne, 

 which implies, other things being equal, 

 a higher grade for the present than for the 

 Neocene channel, while, as we have seen, 

 the reverse is the case. The broad channels 

 and large sand and gravel deposits of the 

 Neocene streams of the Sierra further north 

 can scarcely be explained on any other 

 hypothesis than of comparatively gentle 

 grades, indicating an old age for the 

 streams, and this must have been likewise 

 true of the Neocene Tuolumne, although in 

 less degree. Assuming that the Neocene 

 Tuolumne had originally a grade at least 

 as low as that of the modern stream, which 

 is evidently yet a young stream, it is clear 

 that the present grade of the Neocene chan- 



nel must have been brought about by a dif- 

 ferential uplift on the east, resulting in a 

 tilting of the range westward. 



On an Orbicular Gahbro from San Diego 

 County, California: Andrew C. Law- 

 son, Berkeley, Cal. 



The rock desci'ibed in this paper is a 

 very basic gabbro in the form of an aggre- 

 gation of spheroids having both radial and 

 concentric structure. The spheroids have 

 an average diameter of about 6 centimeters, 

 but are mostly somewhat deformed in shape. 

 The core of these spheroids is a granular 

 gabbro and the space between the spheroids 

 is of a similar character. An analysis of 

 the rock is given. 



A Geological Section of the Middle Coast 

 Banges of California: Andrew C. Law- 

 son. 



The paper is an attempt to summarize 

 recently acquired information as to the 

 sequence of formations and their respective 

 volumes of sediments in the Middle Coast 

 Ranges of California. The results given for 

 the thiclaiess are approximations suffi- 

 ciently close to afford a general idea of the 

 section. Other features of the paper are 

 the subdivision of the Franciscan into seven 

 stratigraphic subdivisions by the recogni- 

 tion of a persistent horizon of f oraminiferal 

 limestone and two important horizons of 

 radiolarian chert; a similar subdivision of 

 the Monterey into seven stages and a sum- 

 mary announcement of the character and 

 history of the post-Monterey Tertiary. The 

 essential features of the paper are given in 

 the following tabulation. 



The Pleistocene Ecology of Southern Cali- 

 fornia: Ralph Arnold, Stanford Uni- 

 versity, California. 



A summary statement of the marine 

 Pleistocene of San Pedro and other locali- 

 ties of southern California with a subdi- 

 vision of the Pleistocene formations partly 

 on the basis of structural unconformities 



