232 PROF. T. G. BONNET ON CEYSTALLTNE SCHISTS AND THEIR 



including a qnartzose variety, can be recognized ; brown mica is 

 abundant. Crystallites ot" rutilo (maximum length about -01 inch), 

 arc numerous, often occurring in elongated nests in the flaky 

 masses of brown mica or in a finely granular, rather dusty -looking 

 mineral (? crushed calcite) and sometimes also with granular quartz. 

 With these are a few grains of tourmaline and not unfrequently 

 small blade-like prisms, about the same length as the rutile, which I 

 would suggest may be kyanite. These rock-fragments appear to be 

 exceptionally rich in microlithic constituents, just as I have noticed 

 is the case with parts of the slides cut from the Piora schists. 



(c) TJlc Jurassic liocls. 



Under the microscope the specimens from both the Lukmanier 

 and the Nufenen Passes present a strong family likeness. The 

 matrix consists of calcite * in rather elongated and somewhat irregu- 

 larly outlined grains (generally less than -01 inch long, not uncom- 

 monly about -005 inch), with a variable quantity of a clear mineral, 

 part of which is quartz, but part is perhaps a silicate, with flakes of 

 a colourless mica, which gives rather brilliant polarization-tints, 

 and with granules, probably of the second mineral described below. 

 Scattered through the matrix is a minutely granular, greyish to 

 blackish, sometimes brownish, powder, the colouring-matter of the 

 rock. There are also occasional grains of pyrite or an iron-oxide, 

 more or less perfect prisms of rutile f, and (rarely) of (?) tourmaline, 

 all of small size. It is very difficult to decide how far the con- 

 stituents are derivative. The calcite, in its present condition, is 

 probably authigeuous, so also may be the quartz ; but not seldom 

 the form of a grain suggests the presence of a fragment as nucleus, 

 which has only received a slight enlargement in situ. In the case 

 also of the mica the evidence is inconclusive. Here, again, it is 



* Mr. J. Chorley, of University College, has kindly determined tlie amount 

 of CaCO.3 in a specimen in which the "knots" and "prisms" were not 

 abundant ; the first which I collected on the nortli side of Scopi. One 

 estimate gave 8272, the other 83*53. Of course, where the included minerals 

 are numerous, the percentage of carbonate in the whole rock would be lower ; 

 but I should say that this was a fair sample of the matrix throughout, and 

 that every specimen which I have examined probably contains over 50 per 

 cent, of carbonate of lime. I have examined the residue of tJiis rock under the 

 microscope ; it consists largely of generally minute granular graphitic matter, 

 with small flakes of a colourless mineral of no definite outline and weak 

 depolarizing power (? inica), sometimes " peppered " with the black dust, and 

 rather numerous acicular microliths, not generally exceeding -002 inch long. Of 

 these there appear to be two varieties — the stouter brownish yellow in colour, 

 probably rutile ; the other lath-like, colourless, extinguishing either parallel 

 or at a very small angle with the sides (? kyanite). Also there are granules of 

 quartz, felspar (?), and possibly zircon. I have not been able, from this study 

 alone, to form any positive conclusion as to the history of the rock. 



t The rutile-crystals occur sporadically, but two or three are in close 

 proximity. Once or twice I found a lai-ge number of rutiles in what appeared to 

 be a small fragment of another rock. This very closely resembles a jDortion of 

 one of the layers rich in rutile in the Dark-mica series. T may add that one 

 or two bi^^s in the matrix resemble garnet, but these are almost ceitainly of 

 fragmentai origin, not authigenous. 



