Fairbanks.i Ana/cite Diabase. 275 



it has a width of about 1,000 feet, and extends in a northwest direc- 

 tion for a number of miles, gradually becoming narrower. The 

 southern portion, exhibiting by far the greatest variation, and pos- 

 sessed of the most interest, is that from which the material for 

 study was collected. 



The second occurrence, which will be described in this paper, 

 has a length of about twelve miles, extending northwest and south- 

 east parallel to the Santa Lucia Range, on the slope of which it 

 lies. The most southerly portion examined is exposed in a cut on 

 the road from Templeton to Cayucos. The next point at which 

 it was observed is at the foot of the grade on the road from Paso 

 Robles to Cambria. At both these localities the sections are not 

 good, and the rock is exceedingly friable and decomposed. Two 

 miles northwest of the last locality, near the old Oceanic quick- 

 silver mine, a deep canon has been eroded across the eruptive 

 body, giving an excellent section. At the southern exposure only 

 one dike was noted. At the middle there are three, while in the 

 canon at the Oceanic mine there are four, the largest being nearly 

 300 feet wide. The dikes, as in the case of the Cuyamas occur- 

 rence, are inclosed in rocks of probable Miocene age. 



CONTACT METAMORPH ISM. 



This phenomenon is very noticeable in the contact rocks of 

 each of the occurrences. In that of the Cuyamas the strata have 

 been tilted up vertically on each side of the dike, and distinctly 

 changed for a distance of 100 feet. In an old tunnel, run in pros- 

 pecting for silver, it is well shown; also in a canon cutting across 

 the dike farther north. At the latter locality a large mass of the 

 country rock appears on the north wall of the canon wholly inclosed 

 in the eruptive. 



Macroscopically the metamorphism appears to consist of an 

 induration and blackening of the soft gray clays and calcareous 

 sandstones, the clays having been changed to a black shining slate, 

 and the incoherent sandstones to hard, slaty masses, giving a ringing 

 sound when struck. The dark color is probably due to the effect 

 of heat on the organic matter contained. 



The nature of the inclosing rocks and the metamorphism 



