134 ME. ALFRED HABKEE ON THE CAEEOCK EELE [May 1 895, 



composition than the normal type. From this it differs mineral- 

 ogically, chiefly in the greater abundance of augite which it con- 

 tains. That mineral builds the usual idiomorphic crystals, but is 

 largely replaced by green hornblende and other substances. We 

 also note the presence of iron ores, which were mentioned as rare, 

 and apatite, which was almost wholly wanting, in the normal type. 

 The idiomorphic zoned felspar-crystals are abundant, and the inter- 

 stitial micropegmatite occupies somewhat less space than formerly. 

 No. 2 has a specific gravity of 2*805, with a silica-percentage of only 

 58 or 60. The augite, in rather large idiomorphic crystals, is 

 somewhat more abundant, and the apatite and iron ores are also 

 more prominent constituents. In addition a little biotite is found. 

 Besides the beautiful micropegmatite which clings about the idio- 

 morphic felspars, there is in places what looks like a kind of micro- 

 graphic arrangement in the destroyed augite and even in the iron 

 ores. The same thing is seen in No. 3, a still more basic rock, of 

 specific gravity 2*925. The augite and its alteration-products are 

 perhaps a little more plentiful, and the same may be said of the 

 iron ores, the apatite-prisms, and the scanty flakes of biotite. The 

 idiomorphic felspars are often seemingly untwinned, but their 

 zonary banding is still marked. The micropegmatite is reduced in 

 quantity, and tends to consist mainly of quartz. On the other 

 hand, there are micrographic intergrowths of felspar and (destroyed) 

 augite. This rock has a very compact, dark aspect in the field, and 

 weathers into spheroids. It seems to represent the actual border 

 of the granophyre-intrusion, for it is in contact with undoubted 

 gabbro, though of somewhat peculiar character. Some brecciation 

 indicates a certain amount of crushing along the line of junction, 

 but there is evidently no break of importance. The gabbro, No. 4, 

 is the extreme basic modification of that rock, its specific gravity 

 being 3*200 and its silica-percentage only 33*4. It exhibits the 

 peculiar metamorphic effects noted in my former paper, such as the 

 abundant production of tremolite, sphene, etc., with the destruction 

 of the original minerals ; but enough remains of the latter to mark 

 the fundamental difference between this rock and the preceding. 

 For instance, the augite of the gabbro is of the pale greyish-brown 

 variety with characteristic basal striation, and always moulds the 

 felspar-crystals. 



In this section we see that, notwithstanding the curious basic 

 modification of the granophyre towards its southern margin, the 

 line of separation between that rock and the gabbro can be drawn 

 with absolute sharpness. The fact that the gabbro becomes pro- 

 gressively more basic towards its northern boundary has already 

 shown us that there is no passage from the one rock to the other in 

 the usual understanding of the words ; we now see that neither 

 chemically nor mineralogically is there a gradual transition from 

 the one intrusion to the other. The silica-percentage of the grano- 

 phyre, for instance, decreases gradually down to about 58, but then 

 the figure drops ahruptly to 33^ in the xiltrabasic gabbro. Again, 

 the granophyre becomes continually richer in augite as we approach 



