SUPPLEMENT I. 



NOTES ON THE GEOLOGY OF THE VICINITY OF 

 MUIR GLACIER. 



BY 



H. P. GUSHING. 



CONTENTS. 



Page. 



General Features 56 



Sedimentary Kocks 57 



The Argillite 57 



The Limestone 59 



Eruptive Rocks , 60 



The Diorites 60 



Quartz-diorite 60 



Later Eruptives 61 



General Features. 



Both aqueous and igneous rocks occur in the vicinity of Muir 

 glacier, and the plutonic rocks belong to two distinct periods. 

 All the rocks of the vicinity have suffered much dynamically, 

 the recent eruptives excepted. The whole series is much shat- 

 tered and fissured. Three sets of fissures are generally readily 

 made out, dividing the rock into small prismatic blocks. These 

 fissure planes are seldom vertical, but present varying angles. 

 Generally they are mere cracks, often filled by infiltration, but 

 sometimes they have a width of several feet. The numerous 

 small dikes of andesitic rock appear to have the same directions 

 as tlie fissure systems, and were probably formed at the same 

 time. Evidence of small faults of comparatively recent origin, 

 involving these dikes and determined by their aid, is occasionally 

 forthcoming, showing a certain amount of disturbance in the 

 region since they were formed. Evidence of earlier faults is dif- 

 ficult to obtain, owing to the homogeneity of the rocks and the 



(56) 



