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University of California. 



[Vol. 2. 



tural features, its volume, its distribution, and its relation to over- 

 lying formations. 



Structural Features. — For the first thousand feet of the exposure 

 of the formation along Skyline Ridge from the point where it is 

 first encountered, the dip of the beds may be observed at numerous 

 outcrops, both on the ridge top and more particularly on the steep 

 upper part of the south slope. In no case are the beds found in 

 their original horizontal attitude. They are tilted at various angles 

 and in variable directions, and a careful plotting of the observable 

 dips will show that the beds are acutely buckled and broken. In 

 spite of this irregularity, however, two facts of importance result 

 from these observations, viz.: (i) That the prevailing direction of 

 the dip is easterly, and that the formation as a whole dips in this 

 direction, notwithstanding local vagaries. (2) That the angle of 

 dip is prevailingly of low value, i. e., that the dip is much nearer to 

 horizontal than it is to the vertical. As soon as we reach the 

 flanks of Sugar Loaf, however, this lowly inclined attitude of the 

 beds and of the formation as a whole abruptly changes. From this 

 point on to the upper limit of the formation the attitude of the beds 

 is continually vertical. We thus see that the minor portion of the 

 formation is abutting obliquely upon the major portion, which 

 makes up the prominent hill called Sugar Loaf. This relation 

 affords us excellent evidence that the formation has been dislocated 

 and that the two portions have been differentially shifted. We thus 

 have presented to us the phenomena of faulting. A minimum 

 value of the amount of dislocation is evidently measured by the 

 thickness of the lowly inclined strata which abut upon the vertical 

 beds. This is practically the measure of the height of the ridge 

 above the road in Telegraph Canon, or about 500 feet; for we find, 

 on following the lower limit of the lowly inclined part of the forma- 

 tion down the south slope of the ridge, that this contact-plane also 

 abuts upon the vertical beds just above the road. The actual 

 amount of the dislocation may be much more than this minimum 

 value. A fault with such an important throw could not terminate 

 or die out within the narrow limits of the width of Skyline Ridge, 

 and we should, therefore, expect to find evidence of its extension 



