600 FRANK D. ADAMS AND J. AUSTEN BANCROFT 



with dimensions of io"Xii"X i\" . Under the microscope the 

 rock is seen to possess a distinct foliation parallel to the broad 

 surface of the slab. All of the columns were cut from this slab with 

 their longer axes parallel to the foliation. In thin sections under 

 the microscope the rock is seen to be composed chiefly of chlorite, 

 talc and dolomite, numerous small crystals and grains of magne- 

 tite, and a few grains of pyrite are also present. The two minerals, 

 chlorite and talc, make up by far the greater portion of the rock, 

 the chlorite being somewhat more abundant than the talc. Both 

 occur as plates and sheaflike aggregates, and both possess a very 

 distinct cleavage parallel to which extinction takes place. The 

 dolomite is present both in large rhombohedral individuals and as 

 small irregular granules which possess a linear arrangement parallel 

 to the foliation of the rock. None of the grains of dolomite show 

 either twinning or strain shadows. Having been cut parallel to the 

 foliation, it is not surprising that the columns of this rock employed 

 in the experiments bulged assymetrically when deformed, and 

 hence a larger number of experiments were made with the steatite 

 than with the other rocks, in order that accurate average results 

 might be secured. 



Slate, New Rockland, Quebec, Canada. — This is a typical fine- 

 grained slate, black in color, uniform in character, and possessing 

 an excellent cleavage. By means of a diamond drill cores were 

 taken perpendicular to the cleavage of the slate, and from these 

 the columns of slate used in the experiments were prepared. 



Under the microscope this slate is found to be composed essen- 

 tially of minute flakes of two minerals, one of which is apparently 

 kaolin and the other muscovite. In general, the kaolin is much 

 more abundant than the muscovite, from which it can be distin- 

 guished in that it possesses a lower double refraction and is not 

 quite so transparent. Within a few extremely narrow bands of the 

 slate the muscovite preponderates. A few minute grains of quartz 

 are interposed between the flakes of muscovite and kaolin. A con- 

 siderable number of very small flakes of black, opaque, carbonaceous 

 matter, abundant, minute, needle-like crystals of rutile, and a very 

 few widely scattered grains of pyrrhotite are also present. The 



