226 IRVING. 



additions except in regard to the interpretation of the observed 

 phenomena. 



The rock seems to be more closely related to the dacites and 

 andesites than to the rhyolites. The outbreak is not pustular 

 but one of the most perfect examples of a laccolite that the 

 region affords. It does not in the least suggest the idea of a 

 " plutonic plug," as Professor Russell, must himself have ad- 

 mitted had he been able to examine it closely. 



In addition to these more perfect laccolitic masses others 

 occur which do not form prominent mountains and whose rela- 

 tions are not so simple. Their laccolitic character seems to be 

 unquestionable, although it has been much modified by faulting 

 and subsequent intrusion. Of these the most important is the 

 large quartz-porphyry mass, at the head of Squaw creek, the 

 highest point of which is War Eagle hill. 



War Eagle Hill Intrusion. 



If we descend into the head of Squaw creek from the B. 

 & M. R. R. we will see that the sides of the deep gorge 

 are here composed of a light brown quartz-porphyry, which 

 stands in abrupt wall-like masses. On top of the hills to 

 the northeast and southwest lie Cambrian shales and sand- 

 stones. From the broad top of the first hill one may descend 

 in all directions and find below the thin capping of shales, 

 solid quartz-porphyry, in whose continuity no break can be 

 detected. On the east the Cambrian may be found forming 

 a thin partition between the porphyry and the Algonkian, 

 and as we trace this around to the north it gradually becomes 

 thinner, until, so far as can be observed, the porphyry rests 

 directly on the Algonkian. Again, in the head of East Squaw 

 creek prospecting tunnels have penetrated a small mass of 

 Cambrian, which lies underneath the porphyry at that point. 

 If now we walk southwest from the head of East Squaw 

 creek we pass up over the porphyry and down to the bed of 

 Squaw creek, and across the same rock until we find the shale 

 covering it on the top of the hill. It is again encountered in a 

 thin sheet on the narrow-gauge railroad and may be seen ly- 



