Vol. 51.] GKANOrHYRE AND THE GRAINSGILL GREISEN. 135 



the Furthergill stream, yet there gives place to a rock containing 

 abundant augite indeed, but of a quite different variety, namely, 

 the aluminous ophitic augite with basal lamellation which we have 

 found to characterize the gahbro-mass throughout its extent. 



Following the line of junction up Furthergill Sike and westward 

 towards Round Knott, we do not always find quite identical rela- 

 tions. Though the abrupt break is not bridged over, there are 

 places where the difference in silica- percentage between the two 

 rocks in contact one with the other would probably be less than that 

 just noted. This is where there has been a certain impregnation 

 of the marginal gabbro by granophyre. 1 So far as my observation 

 goes, this is exceptional, and does not extend more than a couple of 

 feet from the actual junction. The anomalous character of these 

 quartz-bearing ulfcrabasic rocks is very striking. One, with a 

 specific gravity of 3*026 to 3-122, is seen in the prominent crag 

 overlooking Furthergill Sike at the spot marked by the letter F on 

 the 6-inch Ordnance map. 



In some places, too, the relations are complicated by apophyses 

 of the granophyre traversing the gabbro. This complication is 

 brought out by a longer traverse across Furthergill Sike, a little above 

 the crag just mentioned. It is not necessary to give full details 

 of this section. The basic modification of the granophyre (a, sp. gr. 

 2-724) is in contact with the highly basic iron-ore-gabbros (/3, sp. gr. 

 3'060, and $, sp. gr. 3*190), but the latter are divided by a tongue 

 of thoroughly acid rock (y, sp. gr. 2-636). 



On the fell above there are only occasional exposures along the 

 line of junction. About 100 yards south of the Carrock Fell sheep- 

 fold is seen a very coarse rock containing columnar black crystals 

 up to 2 inches in length. These are, in the main, of hornblende, 

 but it is not clear to what extent that mineral is derivative from 

 augite. Certainly in some cases, in this and other specimens, horn- 

 blende occurs with its own proper crystal-forms. Biotite, iron ores, 

 and apatite are also seen in a hand-specimen, while the microscope 

 shows a micrographic groundmass clinging round the large idio- 

 morphic felspars. Augite occurs also both in idiomorphic crystals, 

 with partial uralitization, and in micrographic intergrowth. This 

 rock, with a specific gravity of 2'738, is not unlike No. 2 of the 

 above section, though perhaps a little more acid. 



About 300 yards west of the summit of Carrock Fell occurs 

 another coarse -textured rock which, on a large scale, shows a 

 curious mottling of pink felspathic and black pyroxenic patches. 

 The idiomorphic felspars here tend to narrow elongated forms. 

 Biotite is present, as well as the abundant augite and hornblende. 

 This rock has a specific gravity of 2-904, and corresponds to No. 3 

 of the section noted above. This and the preceding evidently belong 

 to the basic margin of the granophyre. The dark ultrabasic gabbro, 

 metamorphosed and partially impregnated with granophyre, is 

 seen in loose blocks, but does not make any show in situ. This is 



1 See my former paper, Quart. Journ. Geol. Soe. vol. 1. (1894) pi. xvii. fig. 6. 



