THE OHEIITY LIMESTONE. 135 



Wis. after the luimbers are from tlie collection of the Wisconsin Geolog'ical 

 Survey. Locations are given from soiitheast corner of the section, in steps 

 of 2,000 per mile. 



1. Tremolitic dolomite. Specimen 9G78 (slide 31G5). From 1850 N., 1075 W., 

 Sec. 22, T. 44 N., R. 5 W., Wis. 



A nuitbrmly grainilai'. grayish white limestone; in appearance very close to 

 marble. 



The thin section is composed chiefly of interlocking grains of dolomite, which 

 often show the characteristic cleavage and twinning. Mingled with the dolomite are 

 quite large blades of tremolite, wliich in many places are more or less decomposed 

 (PI. XVI, Fig. 1). 



2. Tremolitic dolomite. Specimen 189 Wr. From N., 1900 W., Sec. 15, T. 44 

 N., R. 5 W., Wis. 



The mass of this loclc is like 1, except that it is of a dark gray color. Cutting 

 through.it are veins of tremolite in very coarse, radiating blades. 



The greater part of the section is like that of 1, but a portion of it is cut from* 

 tlie vein of tremolite, which mat(^rial occurs in radiating clusters of (piitc large sized 

 brilliantly polarizing blades. 



3. Quartz rock. Specimen 907(i (slide 3103). From 1900 N., 1300 W., Sec. 22, 

 T, 44 N., R. 5 W., Wis. 



A finely granular, very friable, snow-white quartz rock, which in the sunlight 

 exhibits innumerable glittering crystal facets. 



The thin section is coniposed of a minutely cry.stalline mass of quartz. The 

 quartz individuals are in large part crystal outlined, and appear to fit against each 

 other perfectly, face to face,, with little or no interlocking. There are usually no 

 vacant spaces between the crystals, but the fragility and pseudo-arenaceous texture of 

 the rock are explained l)y its jiecnliar make-up. No amorplious silica is present, nor 

 is there any evidence that tlie crystals have been produced by the enlargement of 

 quartz fragments, as in ordinary quartzites. 



4. Tremolitic dolonute. Siieciinen 9054 (slide 3101). From 1400 N., 1000 W., 

 Sec. 24, T. 44 N., R. 4 W., Wis. 



This rock ditt'ers from 1 in that a portion of it is of a decided greenish color. 

 The section differs IVoni that of 1 in that tlie tremolite is almost as ahundant a" 

 the dolomite. 



5. Dolomite. Specimen 9053 (slide 3100). From 1300 N., 1000 W., Sec. 24, 1 

 44 N., R. 4 W., Wis. 



The rock is fine grained, uniformly granular, and of a gray color. 

 The thin section is comi)osed wholly of a finely and evenly granular aggregatioi 

 of dolomite individuals. 



6. Tremolitic dolomite. Sp.'cinnms 9531 (slide 3138), 1421 Wis. (slide 251). Frore 

 1440 N., 1200 W., Sec. 14, T. 44 N., R. 3 W., Wis. 



