THE QUARTZ-8I;ATE MEMBER. 1G7 



39. Quartzites, tVoiii the hottom of the (i)uartz-slatc inciiihor, ininu'diatoly Itonoath 

 40. Siu'ciiiifiis 944-1 (slide M'Mi), 7507 (slide 1952). Prom 19S5 N., 750 W., Sec. 15, T. 

 47 N., 11. 45 W., Michigan. 



The si>e('iiiiens and thin sections resemble closely those of 24. 



40. (Ihert-coiigionierate, from near the base of the (inartz-slate member, and 

 immediately beneath 7505 (41). Specimens 9449 (slide ;Ji;!4), 7500 (slide 1951). From 

 1998 N., 750 W., Sec. 15, T. 47 N., R. 45 W., Michigan. 



The matrix of this rock is fine grained, compact, and of a gray color. In this 

 matrix are very numerous rounded pebbles of chert, which are sometimes several 

 incites in diameter. 



In the thin sections the mixtrix of this conglomerate is seen to be composed of 

 materials of two degrees of fineness. The liner appears, as is general with the slates 

 of this member, to be composed of minutely crystalline, and, at times, even an amor- 

 phous silica, with which are mingled some kaolin and ferrite. The coarser jwrtion of 

 the matrix is distinctly fragmental and is made ui^ wholly of quartz pieces, nearly all 

 of which show the usual secondary enlargements. The pebbles of the c(mglomerate 

 are wholly of a chert identical with that characteristic of the limestone mendjer, as 

 previously described. They are seen to be made up of an intimate mixture of a 

 minutely crystalline and an amorphous or opaline silica. 



41. Sandstone, from a very low horizon. Specimen 7505 (slide 1948) From 

 N., 750 W., Sec. 10, T. 47 N., R. 45 W., Michigan. 



This rock in sitecimen and thin section resendjles .'{5 from the IJlack river section. 



42. Argillaceous slates or shales, from a low horizon. Specimens 7502 (slide 

 1944), from 2 N., 177 W.; 750;{ (slide 1945), from 10 N., 177 W., Sec. 10, T. 47 N., R. 

 45 W., Michigan. 



Aphanitic, highly laminated slates or shales having a strong clayey odor, and 

 colors varying from reddish l)rown to greenish gray. 



The thin sectiinis differ from those ot 43 in that the fragmental i)articles of (juartz 

 and feldspar are now insignificant in quantity, the clayey matrix assuming a relatively 

 important role. 



43. Argillaceous slates or shales. Specimens 7504 (slide 1940), from 1985 N., 4.50 

 W.; 75(»5a (slide 1949), from N., 7.50 W., Sees. 10 and 15, T. 47 X., R. 45 W., .Michigan. 



Compact clayey slates or shales, not always showing the lines of sedimentation ; 

 in cohu' \arying from gieeuish gray to reddish brown, some specimens presenting both 

 colors. 



The tliin sections show small fragiiu^nts of quartz and feldspar, the former the 

 more abundant and commonly provided with s(^condary eidargements, imbedded in a 

 groundmass composed of ferrite, chlorite, kaolin, and minutely crystalline silica. (PL 

 XIX, Fig. 4.) 



44. Sericitic graywaitkes, fiom a low horizon. Si)ecimens 0432 (.slide 3130), from 

 1925 N., 1915 VV.; 94;55 (slide ;il.;2), from ]9;55 N., 1940 W.: 9430 (slide 3008). fiom 



