62 



DEPARTMENT OF THE INTERIOR 



2 GEORGE V, A. 1912 



section of the dolomite is incomplete; with all its typical characters it dis- 

 appears, to the eastward, beneath the stream gravels and glacial deposits 

 surrounding the lake. (Figures 5 and 6.) 



Throughout its whole observed thickness of 200 feet the formation consists 

 of an exceptionally strong and massive, dark gray carbonate rock, weathering 

 dark gray to brownish gray and sometimes buff. In the field the rock has a 

 most deceptive resemblance to a homogeneous, thick-bedded argillite. It effer- 

 vesces but slightly in cold dilute acid, and the essential carbonate character 



Figure 7. — Diagrammatic drawing from thin section of Water-ton dolo- 

 mite, showing middle part of a lense of orthoclase in interlocking 

 granules. Rhombohedra of dolomite are embedded in the anhedral 

 dolomite which forms most of the l-ock. The cleavages shown in the 

 carbonate are diagrammatic only and in reality are seldom visible. 

 The black spots represent carbonaceous matter. Highly magnified ; 

 diameter of circle 0' 15 mm. 



was not suspected until the more careful laboratory study was put on the rock. 

 The thin section showed immediately that it is largely composed of carbonate 

 grains. Their size is very small, the diameters steadily averaging about 0-02 

 mm., with a few grains reaching twice or thrice that diameter. These grains 

 are sometimes knit together in a thorough, interlocking manner but more often 



