312 ME. ALFRED HARKER ON THE GABBRO [Aug. 1894, 



of Rosenbusch. Later he described both this rock and the gabbro 

 (a quartz-bearing variety), stating that the one passes into the other 

 by insensible gradations. 1 



In 1889 Mr. T. T. Groom 2 pointed out the occurrence on Carrock 

 Fell of another type of rock, a tachylyte, in thin veins, cutting the 

 gabbro, but considered to be connected with it. The same writer 

 reasserted the existence of all transitional stages between the acid 

 granophyre and the basic gabbro, and this passage seems to have 

 been generally accepted. 3 



The references here given cover all the contributions of importance 

 dealing with the subject of this paper since the early writings of 

 Otley, Sedgwick, and others. Ward's work is embodied in the map 

 of the Geological Survey. 4 He showed that rocks answering to the 

 chief types which he recognized in Carrock Fell occur to the west 

 as far as Roughten Gill. The sketch-map which accompanies the 

 present paper (PL XVI.) differs from his as regards the boundaries 

 of some of these intrusions ; but in some parts, e. g. north and north- 

 west of Carrock Fell itself, the want of exposures makes any pre- 

 cision impossible. This, however, does not affect the objects of the 

 present study. 



Carrock Fell itself is made up of an acid rock, which we may call 

 ' granophyre,' since it usually shows very beautifully the granophyric 

 structure of Rosenbusch. A similar rock is found beyond the con- 

 cealed ground to the north-west, at Rae Crags ; also at the head of 

 Brandy Gill. From the latter place the rock is probably continuous, 

 though never seen clearly in situ, to the exposures in the upper part 

 of Roughten Gill and its feeders. Intrusions of granophyre, 

 probably of the nature of minor offshoots, are also seen in Arm o' 

 Grain and Thief Gills. 



The other of the two chief rocks to be distinguished, which will 

 be spoken of as the ' gabbro,' is seen south of Carrock Fell, as far as 

 Mosedale village, and extends westward to Brandy Gill and Arm 

 o' Grain, where the exposures in the gills show it alternating with 

 the granophyre. A similar rock occurs in Roughten Gill and also 

 higher up, in Thief Gills, wbere, however, it is much decomposed. 

 The southern boundary of the main body of gabbro, from Mosedale 

 village to Brandy Gill, is certainly, as surmised by Ward, a faulted 

 one. The line between the gabbro and the granophyre runs from 

 the upper part of Furthergill in a W.N.W. direction to a point 

 about 200 yards east of Round Knott. Despite the alleged transi- 

 tion, which I shall discuss below, there is no difficulty in fixing 

 this line sharply, wherever exposures occur ; but it may be noted 

 that a north-and-south traverse across Furthergill crosses alterna- 

 tions of the two rocks, which are naturally explained as due to 

 offshoots of the newer one penetrating the older. 



1 ' Biitish Petrography,' 1888, p. 178. 



2 Quart. Journ. Gaol. Soc. vol. xlv. (1889) pp. 298-304. 



3 See, for example, Zirkel, ' Lebrbuch der Petrograpbie,' 2nd ed. 1893, p. 781. 



4 England and Wales, 101 N.E. (New Series, 23). This map is dated 1890, 

 but was not apparently issued to the public before 1893. 



