1895. ] NEW YORK ACADEMY OF SCIENCES. 25 
in part as dikes.* The eruptives were studied by Dr. Geo. H. 
Williams,} who determined the main intrusion to be of quartz- 
diorite, while both acidic and basic dikes occurred, the latter 
largely predominating, and being in large part diabases. The 
argillites were the oldest rocks found; the quartz-diorite intru- 
sion was subsequent to the deposition of the limestone, and the 
dikes cut all the other rocks. 
The region is a disturbed one, the time of the disturbance 
antedating the formation of the dikes, for the most part. The 
rocks have undergone regional metamorphism, have been tilted, 
folded, faulted and fractured. The argillites are baked into 
hard, flinty rocks, which break under the hammer with great 
difficulty and have totally lost all tendency to split on the old 
bedding pianes, which are only traceable by means of occasional 
color variations in the different layers. The limestone is also 
greatly metamorphosed. ‘The whole series is cut up into small 
blocks by intersecting systems of joints. The tremendous 
dynamic strains which have acted upon the rocks are made 
clearly manifest when the quartz-diorite is examined in thin 
section under the microscope. On the other hand, no such 
effects are disclosed by the study of the dike rocks. A certain 
amount of disturbance since the time of dike formation is made 
apparent by the occasional faulting of a dike, but-so far as ob- 
served the throw of these later faults is always tolerably insig- 
nificant in amount. 
The Argillites.—The argillitic rocks have a wide distribution 
around the eastern side of the Muir glacier basin and also form 
the mountains adjacent to Muir inlet. They present three main 
phases : 
1. Very hard, fine grained argillo-siliceous bands, gray to 
brown in color, occasionally approaching quartzite in character. 
2, Blue to black, somewhat slaty recks, nearly as hard as the 
first and equally fine grained, less siliceous, but containing a 
slight amount of calcareous matter. These two varieties con- 
stitute the main portion of the mass. They separate into small, 
rectangular blocks along the joint planes, but show no tendency 
to split along the bedding planes. The blocks are somewhat 
cemented together by wide-spread secondary calcite in the 
joints, presumably derived largely from the rocks themselves. 
Disintegration takes place with amazing rapidity, as shown by 
the enormous piles of morainic matter furnished to the tribu- 
taries of Muir glacier whose valleys are adjoined by mountains 
of argillite, and by the massive talus heaps that are rapidiy 
* Nat. Geog. Mag., Vol. IV., pp. 57-62. 
7 Nat. Geog. Mag., Vol. IV., pp. 65-74. 
