40 Grandall — Santa Clara Valley Region in California. 



Orossby Ranch, Arroyo del Yalle. — Interest in the Arroyo 



del Yalle beds led to a measurement of the Cretaceous section 

 at that place. The Jordan ranch beds were taken as a standard 

 horizon, and the thickness of the series determined on both 

 sides of these beds. Southwest of the Jordan ranch beds, there 

 are black shales and hard sandstones. On the ridge due west 

 of Jordan ranch, there is a massive conglomerate, the pebbles 

 of which consist of granite, quartz porphyry, and similar rocks. 

 This conglomerate in places is very hard and quartzitic. The 

 shales, sandstones, and conglomerates are very similar, lithologi- 

 cally, to the Knoxville beds in the adjoining Pleasanton region. 

 Search for fossils brought no results, but at a ranch in the 

 canyon the writer was shown a collection of shells from the 

 surrounding hills. One of these rock specimens contained gas- 

 tropods and Yenus-like shells which were in rock that resembled 

 the yellow sandstone at the Jordan ranch. Another piece of 

 hard black shale contained Aucella Piochi Gabb. The exact 

 location is unknown, but it came from beds already classified, 

 in field work with the Knoxville, because of its distinctive 

 tilhologic character and its dissimilarity to the overlying Upper 

 Cretaceous. In no place was an actual contact found between 

 the Upper Cretaceous and the Knoxville, but wherever the 

 line was crossed the dips and structure indicated conformable 

 deposition. The Knoxville beds rest directly upon the older 

 Franciscan rocks, containing schists, jaspers, serpentines and 

 igneous intrusives. In no place was any actual contact observed 

 between the Knoxville and the Franciscan. Here, as in other 

 places, the change from massive Cretaceous beds with good dips 

 everywhere, to crushed sandstones, schists, serpentines, and in- 

 truded igneous rocks, is marked. 



A number of sections were run across the Knoxville and 

 Upper Cretaceous beds. The conditions for determining sec- 

 tions are not good, because the Knoxville is covered in most of 

 the area by Upper Cretaceous and the Upper Cretaceous is in 

 turn overlain by Pliocene or Pleistocene gravels. The thick- 

 ness of the Knoxville was found to be about four thousaud feet, 

 the line between this horizon and the Upper Cretaceous being 

 determined arbitrarily by lithological differences in sandstones 

 and shales. 



With the Jordan ranch beds as a fixed horizon, the thickness 

 of Upper Cretaceous was found to be about four thousand feet. 

 The bed from which the fauna was collected by Dr. L. G. 

 Yates and Dr. J. P. Smith is in the middle of this section. 

 The fauna given here shows more affinity with the Horsetown 

 than with the Chico, and still there are two thousand feet of 

 sandstone below these beds and above the Knoxville. 



As far as evidence of structure goes, the beds assigned to the 



