NOXCONFOUMITY BELOW THE CHIOO. 191 



furiiished by the very best local exposures of unconformable contacts; f()r 

 every geolog-ist must liave observed cases where unconformable exposures 

 are closely simulated by local ftiults Could it be proved that the under- 

 lying- mass is of greater age than the Knoxville, the evidence would never- 

 theless indicate a non-conformity between the Chico and the Knoxville, 

 unless it could be shown that the convulsion which has so marvelously 

 crushed the Knoxville Ijeds, at least from Clear Lake to the neighborhood 

 of New Almaden and again at San Luis Obispo, was unfelt at New Idria, 

 which it would be difficult to do, in view of the fact that the comparatively 

 gentle Post-Miocene upheaval certainly extended throughout the Coast 

 Ranges of California and Oregon. 



Mt. Diablo and tlie surrounding country consist of a core of metamor- 

 pliic rock inclosed nearly or quite quaquaversally ])y rocks of Chico and 

 Tertiary age. The core is highly contoi'ted and for the most part is in an 

 extremely metamorphosed condition, though here and there it is compara- 

 tively fresh and in some cases contains Aiicella and associated fossils. The 

 overlying Chico, Tcjon, and Miocene strata are tilted, but otherwise com- 

 paratively undisturbed. Over wide areas these three series seem to be per- 

 fectly conformable, nor have I seen an}' case on the Pacific Coast where 

 there seems any ground for suspecting a non-conformity within tliese limits. 

 Mr. Turner spent several da3''s in this region, collecting fossils from various 

 beds and searching for some exposure in which the relations of the Knox- 

 ville beds and the Chico could be well made out. The result was negative, 

 no exposure being detected from which a non-conformity could be conclu- 

 sively established. On the other hand, the structure is much more easily 

 accounted for by supposing a non-conformity to exist than by assuming 

 conformity. The upturned edges of the more recent strata form long, 

 smooth curves, enveloping the plicated and metamorphosed core, and no- 

 where was there any metamorphism in the strata identified as Chico. 



On the coast in Sonoma County, about two miles below Ft. Ross, there 

 is a sharp contact between the Wallala beds and the metamorphic, serpen 

 tinized rock which extends from this point to below the Russian River, if not 

 to the Golden Gate. Passing back into the hills, the Wallala beds are found 

 capping the first range of elevations op'po.site portions of the sliore, which 



