138 MR. ALFRED HARKER OK THE CARROCK: EELL [May 1 895, 



Without much success I have examined the accounts of several 

 foreign areas for phenomena corresponding with those seen at Carrock 

 Fell. The Lake Superior region at once suggested itself as one in 

 which both gabbros and acid rocks are largely developed, the latter 

 being apparently as a rule posterior in date to the former. The 

 varied groups of gabbros, which there occupy large tracts of country 

 and have been described by several American geologists, offer some 

 curious points of resemblance to the Carrock Fell gabbros. Among 

 these features may be mentioned the wide variations met with in 

 the group as a whole, the local variations marked by differences in 

 the relative proportions of the several constituent minerals, the 

 banded or quasi-stratified arrangement of different types in some 

 localities, the existence of ultrabasic modifications extraordinarily 

 rich in titaniferous iron ores, and the presence in other varieties of 

 orthoclase and micropegmatite. The acid rocks, described under 

 such names as augite-syenite, soda-granite, quartz-keratophyre, 

 ' red rock,' etc., are characterized sometimes by biotite, sometimes by 

 augite. Structurally a large number of them seem to be granophyres, 

 and to agree very closely with Lake District examples. 



At one locality, Pigeon Point in Minnesota, Mr. W. S. Bayley 

 has described some remarkable features at the junction of an olivine- 

 gabbro with a granophy re (' quartz-keratophyre'). 1 Between the 

 two there occurs a zone of rocks chemically intermediate between 

 them and becoming progressively more basic from the side of the 

 granophyre to that of the gabbro. From his examination the author 

 regarded ' the intermediate rock as due to the fusion and re- 

 crystallization of the materials of both the [granophyre] and the 

 gabbro, in consequence of the irruption of one of these rocks into 

 the other at some considerable depth below the surface of the earth, 

 where the conditions were such as to produce a rock with the 

 characteristics of a plutonic rock.' Subsequently he modified this 

 view, and came to the conclusion that the granophyre ' is a product 

 of contact-action between the gabbro and the bedded rocks,' and 

 has arisen from the fusion of the latter (slates and quartzites). 2 

 The field-evidence on which this change of opinion is based seems 

 to be by no means convincing, and I venture to think that the 

 author's earlier conclusion is not seriously shaken. It may be 

 remarked that, whatever the interpretation of the facts may be, 

 Pigeon Point is probably not the only place where such relations will 

 be found. Bayley points out that the red rocks which R. D. Irving 

 styled augite-syenites, etc., are in part like the normal granophyre 

 of Pigeon Point, in part like the intermediate types there observed, 

 and those of the latter division ' are always, so far as could be 

 determined, in close association with gabbro.' Some of the rocks 

 figured by Irving 3 closely resemble slides in my collection from the 

 basic margin of the Carrock Fell granophyre, though not its most 

 basic part. 



1 Amer. Journ. Sci. ser. 3, vol. xxxvii. (1889) pp. 54-63. 



2 Ibid. vol. xxxix. (1890) pp. 273-280. 



3 ' The Copper-bearing Rocks of Lake Superior,' Monogr. U.S. Greol. Surv. 

 vol. v. (1883). See especially pis. xiv., xv. 



