GEOLOGY AND PALEONTOLOGY 21 



The larger dikes are of a coarse-grained diorite, varying 

 to a hornblende-gabbro (74) in some of its phases, show- 

 ing large hornblende crystals in a matrix of basic plagio- 

 clase and colorless augite. These larger dikes branch and 

 send off fine-grained dikes of compact diorite (73) and 

 quartz-diorite-porphyry (75). 



All these dikes have narrow contact zones where they 

 cut the limestones, which contain brownish garnet, pale 

 green pyroxene and needles of tremolite in confused ag- 

 gregates. 



The same limestones make magnificent cliffs on the 

 west side of the bay, near the Indian village in Queen 

 Inlet; the white rock is everywhere most intricately cut 

 by the dark diorite dikes. 



On the western point of Reid Glacier the country rock 

 is granite, a rock not before reported from this region. 

 It is coarse-grained (61), with large pinkish orthoclase 

 crystals and sugary quartz grains, the original hornblende 

 being largely altered to chlorite. Plagioclase feldspar is 

 very subordinate. There is some titanite and a small 

 amount of zircon. 



The granite is cut by a succession of dike rocks, the 

 earliest of which appears to be a greenish aphanitic quartz- 

 porphyry (59) of almost flinty appearance. Of later date 

 are a succession of intrusions of rocks similar to those 

 described from the eastern point; fine-grained compact 

 diorites and diorite-porphyries in mostly narrow dikes; 

 and last of all, an intrusion of quartz diorite, similar in 

 appearance to the tonalite so abundant farther down the 

 bay, which has invaded the whole series and often brec- 

 ciated the black dikes so that the whole mass looks like a 

 mosaic. 



One of the most striking rocks collected in Glacier Bay 

 is a very coarsely porphyritic diorite found only as a 

 boulder on the shore in Hugh Miller Inlet, near the 



