298 QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



four hundred feet from the mouth of the tunnel, a cliange takes place. 

 Instead of the heavy sandstone beds with an occasional seam of shale, the 

 thin, indurated strata so prevalent in the Knoxville series make their appear- 

 ance. Instead of being flat like the sandstones or so little flexed that the 

 curvature is insensible in the width of the tunnel, these thin-bedded rocks 

 are almost everywhere greatly contorted, and for a considerable distance 

 the tunnel is driven through an angle of flexure so sharp that the strata 

 coming in at the roof in one direction pass out at the floor in another, dif- 

 fering from the first by 90°. This sudden transition from uncontorted to 

 closely flexed strata and from soft sandstones to .siliceous, thin-bedded 

 rocks certainly suggests a non-conformity most forcibly. Indeed I know 

 of no other theory which seems adequate to explain the circumstances; 

 but along the actual contact motion has taken place and in i-egions of great 

 disturbance the results of faulting sometimes closely simulate the aspect of 

 non-conformity. From this exposure alone, therefore, I should be unwill- 

 ing to pronounce upon the structure. 



While there is no single exposure at New Idria from which a non-con- 

 formity can be demonstrated, there are many which are most satisfactoril}- 

 explained by the supposition of a lack of conformity; indeed, when once 

 the idea of a break in the continuity of sedimentation is suggested, a mere 

 inspectiou of the country from any higher points affords the experienced 

 geologist strong evidence in its favor. The transition from the crumpled, 

 chaotic, metamorphic rocks to the gently undulating sandstone beds is too 

 complete and too abrupt to fit easily into any other theory of structure. 



There is much other structural evidence in the Coast Ranges, both 

 direct and indirect, besides that obtained at New Idria, of this extremely 

 important non-conformity. Its existence is also an inevitable concomitant 

 of the time relations of the two sets of strata involved, for between the 

 period of the Knoxville beds and that of the Chico there is a gap of hun- 

 dreds of thousands of years. 



It would have been nearly impossible to work out the extremely 

 important structural geology of this district without a topographical map of 

 great accuracy. The map prepared for this report by Mr. J. D. Hoffmann 

 is entirely satisfactory in this respect. It may be depended upon for every 



