September 21, 1906.] 



SCIENCE. 



369 



A new point in regard to the theory of 

 the formation of water-laid glacial deposits 

 is believed to be as follows : When the mar- 

 gin of the ice-sheet was retreating by the 

 annual summer melting faster than ice was 

 supplied, the ice remained longest in the 

 valleys. Masses of ice would thus be left 

 in the deeper valleys which would rise 

 many feet above the surrounding hills. 

 Between these ice masses standing water 

 would occur either as arms of the ocean 

 or as ice-dammed glacial lakes between 

 these ice-blocks. In these bodies of stand- 

 ing water the streams from the melting ice 

 would deposit their sand and gravel, and 

 at the point where the streams issued from 

 the ice there would be eskers and ice-con- 

 tact slopes. These latter deposits would 

 contain the larger materials, and the fine 

 sand would be found farthest from the 

 point where the streams issued from the 

 ice. Where the supply of rock waste was 

 sufficient to fill up the space lying between 

 these ice-blocks, a flat topped delta-terrace 

 would be formed; where the supply was 

 not sufficient to fill up the water body, 

 lobes would occur. These lobes would pro- 

 ject into the water body, and from the axis 

 of the arched layers as shown in sections, 

 the direction of flow taken by a given 

 glacial distributary may be discovered. 



In this deposit, therefore, the lobes at the 

 northwest corner show that the sand of 

 which they are built was coming from the 

 southeast. The arched layers shown in 

 the sections at the southwest corner of this 

 deposit indicate that the material there 

 found came from the northeast. Other 

 sections of this delta-terrace at Brewsters 

 Neck, as revealed by the excavations made 

 for the State Hospital, show that in the 

 center of the deposit there were alternating 

 currents coming from both the east and 

 the west. 



The author believes from the facts shown 



by these recent cuttings and from the facts 

 which have long been recognized from the 

 surface form, that this deposit was built 

 by streams issuing from two blocks of ice, 

 one of these blocks occupying the valley of 

 the glacial Thames, the other occupying 

 the valley of the tributary of the Thames 

 River which flowed through the Poque- 

 tanock Valley. The slope of the surface 

 of this delta-terrace indicates that the last 

 source of the material was from the Poque- 

 tanock ice-block on the east. 



Notes on the Geology of the Guaynopita, 

 Chihuahua, Mexico, Mining District: Dr. 

 E. 0. HovEY, American Museum of Nat- 

 ural History, New York. (Illustrated 

 with lantern slides.) 



The Guaynopita district lies in the heart 

 of the Western Sierra Madre in northern 

 Mexico. It shows a series of Cretaceous 

 limestone and schist and gneiss overlain by 

 volcanic rocks (andesites) and invaded by 

 granite intrusions. Later volcanics (basalt, 

 andesites and rhyolites) have supervened, 

 basins have been filled with sandstones and 

 conglomerates, and the whole region has 

 been deeply dissected by the Aros and its 

 tributaries. 



Dr. Hovey's paper was discussed by 

 Messrs. A. C. Lane and C. E. Dryer. 



The Relations of the Drainage of the Santa 



Clara Valley, California, to that of the 



Pajaro River: Professor J. C. Beanner, 



Stanford University. 



Several years ago Dr. Joseph Le Conte 



advanced the theory that the drainage of 



the Sacramento Valley of California 



formerly entered the Pacific Ocean through 



the Bay of Monterey instead of through the 



Golden Gate as it does at present. This 



theory was based chiefly upon the absence 



of a submerged channel outside of _ the 



Golden Gate and the presence of such a 



channel in the Bay of Monterey. Later 



