WHITE HATJSE AND GEEAT COCKUP. 511 



somewhat similar to those mentioned above ; two or three of the 

 same are much stained with clotted limonite, or contain small crystals 

 of iron oxide.^ Next in quantity to the felspar is a mineral of 

 rather irregular, but sometimes rectilinear outline ; most of it shows 

 one strong parallel cleavage ; occasionally, however, there is more 

 than one direction of cleavage, neither being so distinct. Much of 

 the mineral is rendered opaque by brown dust ; in the clearer part 

 this has a very feeble depolarizing effect, or is wholly inert. The 

 cleavage-planes in the former examples are sometimes separated by 

 a narrow lenticular space (as occasionally seen in mica), occupied by 

 microliths, bright tinted with crossed nicols. It is almost impossible 

 to determine the relation of the extinction to the cleavage-planes, 

 because so little light passes through in any position, but I think it 

 is not parallel with them. On the whole I feel certain the mineral 

 was not mica, but augite (chiefly diallage). 



" Hence the rock originally, in all probability, was a variety of 

 dolerite, and, so far as I can judge, not a very basic variety — cer- 

 tainly not a picrite. I should have said there are some grains of 

 iron oxide, now probably limonite, and perhaps a little apatite." 



This mass of altered dolerite very probably issued originally from 

 the same vent as that which at a later period discharged the dioritic 

 picrite ; the intense alteration that has taken place in the former 

 being due in all probability to contact with the latter. 



The exposures of dioritic picrite are too small to admit of any 

 difference being traced between the outer margins and the central 

 portions of the two masses, but a considerable amount of change has 

 been produced in the surrounding rocks. On White Hause the dioritic 

 picrite is succeeded on the eastern side by a schistose rock, which has 

 clearly at one time been sedimentary, but is now almost crystalline in 

 its nature. This schist is light grey in colour, moderately hard, and 

 splits without much difficulty. In some places the surface is much 

 weathered. A slide, Wo. 3, was cut from this rock, but unfortu- 

 nately it is too thick, and Prof. Bonney was unable to make much 

 of it ; he states, however, that " there is a structure resembling 

 incipient foliation or fluxion ; there are also small patches of rather 

 peculiar structure composed of some carbonate (probably calcite), 

 some crystals of oblong form, now almost opaque, and probably 

 some hornblende." 



White Hause is on the margin of the area affected by the influence 

 of the Skiddaw Granite, and crystals of chiastolite make their 

 appearance in the Skiddaw Slate ' about 200 yards south of the 

 dioritic picrite ; proceeding 400 yards farther in the same direction, 

 Dash Waterfall may be seen plunging over an escarpment of spotted 

 schist. It is difficult to say, howSver, how much, if any, of this 

 change may be due to contact with the picrite, or whether it is due 

 solely to contact with the Skiddaw Granite. 



On the north-eastern, northern, and north-western sides of the 

 dioritic picrite on Great Cockup, a bed of grit which marks one of the 



} These may possibly represent another mineral. 



