154 arnold and anderson recent stream conglomerate 



Occurrences Elsewhere 



Similar deposits of stream conglomerate have not been observed along- 

 other streams in the neighboring region, although the conditions appear 

 to be favorable along others that head in areas of serpentine and the 

 associated metamorphic rocks. Another instance of the formation of 

 hard conglomerate deposits other than travertine b)^ a stream along its 

 bed has been noted elsewhere by the jnnior author. This is in the 

 Diablo range about 100 miles northwest of White creek, along the Arroyo 

 Mocho soiith of Tesla, in Alameda county, and is a very similar case in 

 which the stream flows out of an area of serpentine and Franciscan meta- 

 morphic rocks from which springs of sweetish tasting water issue. The 

 region is comparatively arid and the stream subject to partial drying up 

 each year. The gravel and sand are cemented into a wide level pave- 

 ment of very hard rock, which retards erosion and causes the stream to 

 descend in a series of little waterfalls. The cement is light colored and 

 probably similar to that of Wliite creek. 



Mr J. S. Diller has observed an instance of the cementing of stream 

 gravel in situ in a way very similar to that described on White creek. It 

 is on Swift creek, a branch of Trinity river, in northern California. The 

 stream runs through an area of serpentine and has formed a deposit of 

 conglomerate for several miles and cut a channel through it. The 

 stream bed is now hardened and the process seems to be continuing. In 

 this instance the conglomerate is formed while the stream still flows 

 \\-ithin the serpentine area. This deposit is well known by the inhabitants 

 of the region as the "cement rock." A similar deposit exists on Stuart 

 creek, a neighboring fork of Trinity river. 0. H. Hershey has made 

 reference to the deposit on Swift creek * and considers it to be t3qDical 

 ijlacial till. He describes it as "an unstratified agglomeration of 

 1)oulders, cobbles, pebbles, sand, silt, and clay," and says that it contains 

 glacially striated boulders, and that it is "slightly cemented by the large 

 constituent of unoxidized magnesian and calcareous salts," which he 

 believes to be derived from the glacial grinding of the serpentine, of 

 which the deposit is largely composed. 



* "Ancient alpine glaciers of the Sierra Costa mountains, in California." Journal of 

 Geology, vol. viii, January-Februarj-, 1900, pp. 40-50. 



