184 QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



the thin-bedded strata show the characteristic contortions accompanied by 

 a fine net-work of veins of siHca. At Mt. Diablo, too, there is abnndant 

 proof of the Knoxville age of the metaniorphic rock. Professor Wliitney, 

 writing before Mr. W. M. Gabb had made his final divisions of the California 

 Cretaceous, mentions the occurrences at Mt. Diablo as conclusive of the 

 Cretaceous age of the metaniorphic rocks, but without enumerating the 

 associated fossils. From an examination of the fossil localities in Mr. 

 Gabb's work, however, it appears certain that these were Aucella etc. An 

 examination which Dr. "White and I undertook for the purpose shows tliat 

 in Bagley Creek, about a mile from the summit, Aucella occurs abundantly 

 close to the edge of the metamorphosed area — indeed, in partially meta- 

 morphosed strata conformable with those extremely altered and in struct- 

 ural relations to them which very clearly indicated the same age. Mr. Tur- 

 ner subsequently found a series of beds, some of wliich had escaped, trans- 

 formation and contained Aucella, though inclosed on both sides by highly 

 metamorphic strata. At ^Etna Springs, in Napa County, near the ^tna and 

 Napa consolidated quicksilver mines, Aucella also occurs in the same un- 

 mistakable relation to the metamorphic rocks. In the examinations descri])ed 

 in this volume, Aucella has been detected in immediate connection with the 

 metamorpliic beds near the St. John's mine, Solano Countv, and in the Santa 

 Lucia Range, near San Luis Obispo. Mr. Gabb furtlier mentions an Aucella 

 locality below the New Almaden mines. I have not succeeded in finding 

 Aucella in tliis region, which, however, in the neighborhood of the area sur- 

 veyed, shows only metamorphic rocks exactly similar to those of 3It. Diablo 

 and Knoxville, Miocene rocks lying unconformably upon the metamorphics 

 and volcanics. It appears substantially certain tlierefore that the Aucelln- 

 bearing beds which Mr. Gabb detected must have belonged to the meta- 

 morphic series. The age of the metamorphic rocks is thus determined at 

 a considerable number of points scattered along the Coast Ranges for a dis- 

 tance of 300 miles, or nearly three-quarters of the entire length of the Coast 

 Range system of mountains. Alcatraz Island, close to San Francisco, consists 

 of metamorphic sandstone and shales not distinguishable from those of San 

 Francisco or of Mt. Diablo. Here Major Elliot discovered an Inoccramus 

 not known to occur elsewhere, considered by j\[r. Gabb and Dr. AVliite as 



