Vol. 50.] OF CAEROCK FELL. 335 



magma, mingling with the fused ultrabasic gabbro, has given rise 

 to abundant micropegmatite, the appearance of which in a rock 

 so rich in iron ores is very remarkable. 1 Beyond this zone of rocks 

 are others produced by the incorporation of molten ultrabasic gabbro 

 into the granophyre magma, but these varieties and the general 

 relations between the gabbro and the granophyre will be more 

 properly discussed in connexion with the latter rock. It will be 

 noticed that the production of chemically intermediate rocks at the 

 junction of a basic and an acid rock, as here recognized, has no 

 resemblance to the injection of solid gabbro by minute veins of 

 granophyre, as described by Prof. Sollas; but phenomena compar- 

 able with those which he has described are also locally found. (See 

 PI. XVII. fig. 6, and explanation.) 



The rocks distinguished at the outset as diabase will not be more 

 fully described. Mineralogically they resemble the gabbro, and 

 they reproduce in a less marked manner some of the same pheno- 

 mena of variation. They have certain special points of interest, 

 but not connected with the subject in hand. The present paper deals 

 specially with the variations exhibited in the large gabbro intrusion. 

 I hope on another occasion to show that the Carrock Fell granophyre 

 also exhibits considerable variations, due to another cause, and that 

 the Grainsgill greisen is the result of a process of differentiation 

 entirely distinct from that discussed in the case of the gabbro. 



EXPLANATION OF THE PLATES. 



Plate XVI. 



Sketch-map of part of the Carrock Fell district, showing variation of gabbro. 

 (Scale : 6 inches = 1 mile). 



An attempt is made here to show the distribution of the several varieties 

 of gabbro and diabase. The criterion used is the specific gravity of the 

 rocks, and the data are shown by figures on the map. These are chiefly in 

 the eastern part of the gabbro area, and the dividing lines farther west are 

 drawn with reference to the general characters of the rocks judged by eye 

 and checked by a certain number of specific-gravity determinations, as shown. 

 The specific gravity of the gabbro is seen to increase rapidly from the central 

 zone to either margin. The rock here termed diabase shows much less variation. 



The remarkable relations between the gabbro and the granophyre are not 

 shown in detail, arid the numerous dykes and veins are not marked. 



The general distribution of the enclosed masses of Eycott lavas is roughly 

 indicated. It would be impossible to represent accurately the intricate relation 

 between these volcanic rocks and the enveloping gabbro. 



Plate XVII. 

 Note. — The figures are magnified 20 diameters, and, except no. 2, are drawn 

 in natural light. The numbers in brackets refer to the slides, which are in 

 the Woodwardian Museum, Cambridge. 



Fig. 1. [79]. Gabbro, White Crags (from Mr. Ward's collection). This shows 

 the dominant pyroxene, an augite with fine lamellation parallel to 

 the basal plane. This is combined with simple twinning parallel to 

 the orthopinacoid, giving the 'herring-bone' structure. The augite 

 is seen to mould the felspar-crystals. See p. 317. 



1 No chemical analysis of this rock has yet been made. The specific gravity 

 of one specimen was as high as 3"122. 



2a2 



