58 H. F. Reid — Studies of Muir ~ Glacier. 



the. larger portion of the series, are bands of nearly ec^ual hard- 

 ness of a blue or black slaty rock, containing a smaller arenaceous 

 admixture than the last, but being somewhat calcareous. The 

 first variety is more abundant in the lower portion of the series, 

 the second in the upper. Both are very homogeneous and fine- 

 grained, and extremely compact. The black variet}'^ weathers to 

 a dark -brown color, the gray to a 3^ellowish broAvn and sandy- 

 looking surface. These give characteristic colors to the moraines 

 in the southeastern portion of the amphitheater, a medial moraine 

 sometimes appearing one color or the other as it is viewed from 

 one side or the other. The extreme hardness of these slates is 

 due to their metamorphosed condition. The degree of meta- 

 morphism is quite uniform throughout. 80 far as can be told by 

 the eye, it has nowhere been carried to a point where recrystal- 

 lization has begun, so that none of these rocks are at all schistose 

 in character. The metamorphism and the numerous fissures 

 which cut these rocks have nearly obliterated the old bedding 

 planes, so that dips are generally most perceptible from a dis- 

 tance, owing to the banded appearance given by the presence of 

 the two varieties. Little or no tendency to split on the original 

 bedding planes is now shown, the fissures determining the shape 

 and size of the blocks, Avhich themselves often display the color 

 bands. These bands are well shown in many places ; for example, 

 on the highly glaciated slopes of mount Wright which face the 

 inlet. 



3. Comparatively thin bands of more fissile, black graphitic 

 slates are found interstratified with the others. These are found 

 at numerous localities, and there are certainly several such bands, 

 though their apparent number may be increased by faulting. 

 They are softer than the other slates, and readily split into thin, 

 even slabs. They become dotted with brown specks on weather- 

 ing. The fissures Avhich intersect the slates are commonly filled, 

 wholly or in part, by crystalline calcite, somewhat binding un- 

 weathered blocks together. This is universally the case with the 

 blue-black slates, and more commonly so with the gray ; but 

 such fillings do not occur in the graphitic slates. This would 

 indicate that the calcareous matter was largely derived from the 

 slates themselves, and that the graphitic slates lack it from hav- 

 ing contained none originally. Generally these fillings are mere 

 films, but occasionally wider fissures occur which contain calcite 

 masses of considerable size. The large blocks of white crvstalline 



