512 PROF. T. G. BOIOTET ON THE SO-CALLED DIOEITE 



connects with the mass on Little Knott. This very probably is cor- 

 rect, but the rock appeared to me limited in area. It is fine-grained 

 and not at all characteristic. It is, however, possible that I may 

 have overlooked some small connecting outcrops lower down the 

 hillside. 



The rock, as seems not seldom to be the case with picrites and 

 the more basic olivine-diabases, varies greatly in character. At the 

 first outcrop on Little Knott the dominant rock (No. I.) is fine- 

 grained, not porphyritic, and not at all like that of the Anglesey 

 boulders, resembling a dioritic rock rich in hornblende and poor in 

 felspar. There is also, near the western end of the area, on its 

 northern side, an outcrop of rock (presumably connected with the 

 main mass and close to the altered Skiddaw Slate) which is very com- 

 pact, of a dull grey colour, more hke a felstone. Then a short distance 

 further east, the ordinary, rather fine-graiued, duU green variety 

 (No. II.) passes gradually in the space of about a yard into a mottled 

 pinkish-grey and dull green rock, like an ordinary syenite or diorite 

 (JSTo. III.). Further down the eastern slope of the hill, about the central 

 part of the exposure, the rock becomes coarser, crystals of hornblende 

 about -2 to -3 inch across, with the characteristic dull green serpen- 

 tinous enclosures, being abundant (No. TV.). Here and there the rock 

 becomes still coarser, the hornblende crystals being -4 or perhaps even 

 •5 inch across, but I did not find any larger than this (N'o. Y.). In 

 one part the bigger crystals are rather crowded together and tend 

 to occur in veinhke bands. The coarser varieties much resemble 

 the rock of the Anglesey boulders, in which, however, the hornblende 

 crj^stals are often slightly larger. The rock of the boulders on the 

 crest of the opposite (eastern) ridge corresponds with the medium 

 variety (ISTo. IV.). 



I have had slides prepared for microscopic examination from each 

 of the above-mentioned varieties of the Little-Knott rock. 



No. I. A granular rock, composed of dark hornblende with grains 

 of a paler green mineral ; the former about -1 inch in diameter. 

 The following minerals are visible under the microscope: — (1) horn- 

 blende, mostly in irregularly formed crystals interrupted by some- 

 what rounded enclosures. Colour generally a rich brown, strongly 

 dichroic. Cleavage well-marked. This passes sometimes rather 

 abruptly, as described on a former occasion, into a pale green rather 

 fibrous variety, smaller flakes of which are scattered about the slide. 

 The enclosures, above described, are mostly occupied by secondary 

 products, in some cases serpentinous, but occasionally a crystal of 

 felspar is included. In the slide, intercrystaUized with the smaller 

 and more altered hornblende, is a fair amount of felspar, which is 

 a good deal decomposed, so that it is difficult to identify the species. 

 It is, however, one of the plagioclastic group. There is a small 

 quantity of a mineral, mentioned in my former paper *, which re- 

 sembles an altered enstatite. Granules of iron peroxide, some epi- 

 dote, a little apatite (?), and quartz, probably secondary, with calcite, 

 and other alteration-products are present. 



* Quart. Journ. Geol. Soc. vol. xxxix. p. 259. 



