THE CHEETY LIMESTONE. 137 



the hand siieciiiu'u of these rocks. In phices a very small quautity of brown iron 

 oxide is present in minute i)articles. (PL XVI, Fig. .3.) 



11. Chert. Specimens 942;3 (slide M)G3), 9424 (slide 3064). From 1740 N., 1075 

 W., Sec. 14, T. 47 N., E. 45 W., Michigan. 



A fine grainetl, ])inkish saccharoidal chert. 



The thin sections are like those last described, except that the silica is more 

 coarsely crystalline. (PI. xvi, Fig. 4.) 



12. Dolomites. Specimens 7486 (slide 1935). From 550 N., W.; 9405 (slide 

 3049). From 450 X., 330 W., Sec. 18, T. 47 N., R. 44 W., Michigan. 



Rocks almost exactly like 6. 



In thin section, as in 6, dolomite is the onlyjniueral of importance, and the 

 general appearance is the same as in tliat slide. A little tremolite is present. 



13. Cherts and dolomites. Specimens 7485 (slide 1934). From 5.")0 N., 300 W.; 

 9407 (slide 3124). From 450 X., 330 W., Sec. 18, T. 47 N., R. 44 W., Michigan. 



Consist of interstratitied fine grained, gray limestone and milky white flinty 

 chert. 



The sections include portions of both chert and limestone. The dolomite is like 

 that of 12; the chert like that of slides 2050 and 3131 in 10. In section .5124 the line 

 of separation between the chert and limestone is seen to be perfectly sharj). (PI. xvi, 

 Fig. 2.) 



14. Chloritic dolomite. Specimen 9404 (slide 3270). From 600 N., 40 W., Sec. 

 18, T. 47 N., R. 44 W., Michigan. ' 



This rock differs from most of the previously described limestones in being of 

 a p.ale green color. 



The thin section is composed chiefly of finely crystalline dohmiite, mingled 

 with which is a subordinate ijuantity of pale green nonpolarizing chlorite. 



15. Dolomite. Specimen 9408 (slide 3050). From 525 X., 1925 W., Sec 17, T. 

 47 N., R. 44 W., Michigan. 



A coarser grained roclc than any of the preceding limestones; of a bright 

 flesh color, with pale green si)ots and bands. 



The thin section differs from 3138 in (> only in being coarser gi'ained, and in 

 containing a minute quantity of ferrite, to the presence of which mineral the pinkish 

 color of the rock is due. " 



10. Chloritic (h)lomite. Specimen 9387 (slide 3041). From 3,50 N., 1550 W., 

 Sec. 17, T. 47 X., R. 44 \V., Michigan. 



This rock diflfers fnmi only in cimtaining streaks of a greenis'i material and 

 in being of a i)inkisli gray color. 



The thin section is like that of 14 except that some ferrite is contained. 



