GENERAL SECTION OF THE HURONIAN. 99 



Feet. 

 10. Yellowish chert in thin and very regular beds, interstratified with layers 

 of green, buff and gray silicious limestone and green and pale-drab 

 silicious slate 400 



9. Quartzite, white, very frequently of a vitreous aspect ; large portions so 



massive as to render observation of dip and strike impossible 2,970 



8. Ked jasper conglomerates, varying, however, from a fine-grained quartzite 

 to a conglomerate with pebbles of colored jaspers, flint and quartz, and 

 ranging in size from that of duck-shot to grape and canister 2,150 



7. Quartzite, red, generally fine granular, sometimes conglomeratic 2,300 



6. Slate conglomerate of the same general character as No, 4, but the pebbles 

 are not so large. It is interstratified with beds of reddish and gray 

 quartzite [silicious schist?] and layers of fine-grained, greenish-black, 

 light olive-green silicious slate, some of which yield hones of a very 

 fine description. Considerable masses of greenstone are interstratified 

 in various parts of the deposit 3,000 



5. Limestone, usually of a compact texture, but sometimes partially granular. 

 The colors are green, drab and dark gray, the latter two prevailing. 

 Occasional beds are dull white, with waxy luster in fresh fractures ; 

 these weather to a yellowish-brown on the exterior and appear to be 

 dolomitic. The whole band is in general thin-bedded, and a diver- 

 sity of characters in the layers, probably arising from the presence of 

 more or less silicious matter, causes the surface of the weathered blocks 

 to present a set of bold but minute ribs of various thicknesses, which, 

 when the beds are much aflfected, as they often are, by diminutive 

 undulations, contortions and dislocations, exhibit on a small scale a 

 beautiful representation of almost all the accidents that occur in strati- 

 fication, aff'ording very excellent ready-made geological models 300 



4. Slate conglomerate, composed of pebbles of gneiss and syenite, held in an 

 argillo-arenaceous cement of a gray or more frequently of a greenish 

 color, the latter arising apparently from the presence of chlorite. The • 

 pebbles, which are of reddish and gray colors, vary greatly in size, be- 

 ing sometimes no larger than swan-shot and at others bowlders rather 

 than pebbles, measuring upwards of a foot in diameter. The propor- 

 tions of these also vary much ; they sometimes constitute nearly the 

 whole mass of the rock, leaving but few interstices for the matrix ; and 

 sometimes, on the contrary, they are so sparingly disseminated that in- 

 tervals of a foot or several feet intervene between them, and each may 

 be still several inches in diameter. With the pebbles of gneiss and 

 syenite are occasionally associated some of different colored jaspers and 

 others of quartz. The matrix appears to pass, on the one hand, into a 

 gray quartzite by an increased proportion of the arenaceous grains, and, 

 on the other, into a thin-bedded, dark greenish, fine-grained slate, which 

 is sometimes very chloritic. A third form assumed by the matrix is 

 one in which it is scarcely distinguishable from a fine-grained green- 

 stone. In this state the stratification is often marked by slight differ- 

 ences of color in the direction of which it is occasionally cleavable; the 

 bands, in other instances, are finely soldered together, but in both cases 

 joints usually prevail, dividing the rock into rhomboidal forms which 

 are sometimes very perfect. Very heavy masses of greenstone are gen- 



