40 University of California Publications in Geology [ VoL 11 



consisting of angular grains of quartz, orthoclase and plagioclase 

 feldspar, embedded in very fine grained material. It is usually mass- 

 ive and in appearance may resemble a fine grained, basic eruptive. 

 The matrix of the Dwyka tillite is much the same. 



The presence of carbon at many places in the Franciscan sand- 

 stone is not opposed to the idea of glacial conditions. Regarding this 

 point Barrell says 



... it may be concluded that the broad association of carbon with sediments 

 which are thoroughly decomposed and leached throughout is the mark of continu- 

 ously rainy climates which are tropic or at least warm temperate ; with sediments 

 imperfectly decomposed and incompletely leached the mark of more or less con- 

 tinuously rainy climates which are in addition cool or cold. 



However, the presence of carbon in the Franciscan sandstone is 

 not inconsistent with a warm, arid climate, as before suggested. Near 

 seams of coal the Franciscan sandstone is soft and unlike the normal 

 rock. 



While the possibility of glacial origin of the Franciscan sandstone 

 is worth consideration, there are certain facts which make this hy- 

 pothesis improbable. 



There is some doubt concerning the true nature of the Jurassic 

 breccias near Colfax. Moody professes to be unable to decide whether 

 these breccias are really glacial or whether they represent deposits 

 laid down on alluvial fans. 



Even though a Jurassic age be ascribed to the Franciscan it does 

 not appear to be the correlative of the Mariposa slates. Diller's work 

 in Oregon, indicates that the Franciscan is post-Mariposa. If the 

 Galiee be the equivalent of the Mariposa, the Franciscan must be 

 either younger or older than the Mariposa. 



The presence of numerous radiolaria in the cherts associated with 

 the sandstone is also opposed to the idea of a glacial climate in Fran- 

 ciscan time. Radiolaria are abundant in tropical waters and while 

 they may live in colder waters they are not abundant there. It is 

 conceivable, however, that under certain special conditions, radiolaria 

 might thrive in waters adjacent to a region subject to glaciation. 



G7 Climate and Terrestrial Deposits, Jour. Geol., vol. 16, p. 268, 1908. 



