HANDVILLE DOLOMITE IF FELCH MOUNTAIN RANGE. 

 Analyses of Bandville dolomite. 



409- 



The outcrops, while often entirely massive, usually possess decided 

 structural features. These are indicated b}^ color banding, by differences 

 in texture, and by the banded arrang-ement of the components. Slight 

 variations in the body color of the rock, proceeding from no distinguishable 

 variation in composition, often occur in alternate parallel layers, which are 

 persistent within the limits of observation. With the color banding often 

 go variations in texture, which, however, are neither so regular nor nearly 

 so persistent. The characteristic form taken by these is in thin layers, 

 which as they continue open out into nodules. Such layers consist of 

 closely i^acked crj^stalline grains, very much coarser than the body of the 

 rock, which have grown normal to the boundaries. Adjacent layers are 

 not strictly parallel and sometimes cross each other. They are believed to 

 represent ancient fracture and slipping surfaces, which followed very closely 

 the original bedding, in which the new carbonate individuals have had 

 room for larger growth. The arrangement of the accessory minerals, 

 especially the tremolite, also is usually a banded one. Layers rich in 

 tremolite alternate with layers poor in tremolite, while within the layers 

 the orientation of the tremolite individuals is usually at random. The 

 structure brought out in these various ways is, on the whole, a parallel 

 structure. It corresponds with the strike and dip in all the localities where 

 these can be independently confirmed by the attitude of the adjacent for- 

 naations, and it also has been tlu-owii into minor folds. 1 therefore regard 

 the structure as having originated partly in chemical differences in the 

 material originally deposited and partly in secondary growths in the open 

 spaces and rubbing zones determined by relative movements along the sur- 

 faces of easiest fracture at the time of the earliest folding, and for both 

 reasons preserving in the subsequent metamorphism the true stratification 

 of the formation. 



