224 GEOLOGY OF THE EUEEKA DISTRICT. 



dike at the north end the limestone stands at angles between 70° and 

 90°, and farther south only 35° to 45°, but for the greater part of the dis- 

 tance along the contact crumpling and metaraorphism have so altered it as 

 to have obliterated all signs of stratification. Owing to the frequency of 

 the secondary dikes this metamorphism of strata is much more noticeable on 

 the east than on the west side. Instances may be seen Avhere the lime- 

 stone is completely altered into a fine crystalline white marble. Nowhere, 

 however, does the alteration of strata produced by heat penetrate the lime- 

 stone for any great distance from the dikes, not even between those which 

 run parallel to each other only a few hundred yards apart. The efi^ects of 

 heat are shown far more on the cooling and crystalhzation of the ihtnisive 

 molten mass than on the cold contact rocks. As the beds recede from the 

 main dike the dip becomes less and less steep, the stratification less 

 obscure, and toward the southern end of the dike the limestones lie nearly 

 horizontal. 



The main porphyry dike in cutting the limestone follows closely 

 the strike of the beds, whereas the branch dikes trending approximately at 

 right angles to the main one run across the strata. The position of the 

 main dike is determined in part by a line of faulting and in part by an anti- 

 clinal fold. South of "Wood Cone, where the dike first makes its app'ear- 

 ance, it trends off" to the southwest along the fault line, maintaining this 

 course until near the summit of the limestone hill Avhich lies midway 

 between the two wagon roads that cross the dike. Here meeting the anti- 

 cline, it curves slightly and follows the axis of the fold to the southeast. 

 This anticline may be traced southward beyond the surface outcrop of the 

 o-ranite-porphyry, as is indicated by the dips and strikes on the map. 

 Alono- the northern end of the dike the amount of displacement can not 

 be determined beyond the fact already stated, that both sides of the fault 

 lie in the Pogonip. Why the secondary dikes should break out approxi- 

 mately at right angles to the main one and not parallel with it, it is diffi- 

 cult to say. It would seem as if lines of least resistance would have been 

 formed parallel with the line of the axial fold and the line of displace- 

 ment along which the main dike reached the surface. On the east side the 

 beds are a pure crystalline limestone, uniform in texture and bluish gray 



