Prof. T. McKenny Hughes — Brecciated Archaean Eock. 501 



occasion ^ discussed this point, and given examples of rocks made 

 up of fragments differing more or less in cliaracter from the 

 surrounding matrix in cases in whicli I was able to ojffer abundant 

 evidence that these rocks owed their fragmental character to breccia- 

 tion in place. I explained the pebble-like form of the fragments 

 by the rounding off of the corners which usually accompanies 

 infiltration from the joint surfaces, and further pointed out how the 

 apparent matrix was derived from the alteration of the more finely 

 comminuted portions of the brecciated mass, and from the decom- 

 position of the outside portion of the larger fragments. 



I am now able, as the result of observations made at various times 

 on the Archaean rocks of the Malvern Hills, to supplement and 

 extend these remarks. 



It might be argued that the modification induced by chemical 

 change within the mass would be likely to affect equally adjoining 

 fragments of the same size, composition, etc., and therefore, that, if 

 the apparently included fragments were of different nature, not 

 only from the matrix but also from one another, this must be accepted 

 as evidence that the mass was made up of bits transported from 

 different rocks and various localities, especially if the pieces could 

 be matched among the members of the underlying series. 



It would be pointed out that a volcanic brecciated conglomerate 

 often seems made up of fragments of rock belonging to the very 

 series in which the agglomerate occurs. 



In the Archaean rock which rises abruptly from the level of the 

 New Eed west of Malvern Link, near the quarries, there are some 

 bands of rock (Fig. A B) answering these conditions, which might 

 easily be taken for a brecciated conglomerate. The included frag- 

 ments are of various kinds, different from the matrix, and also unlike 

 one another. Some are coarse light-coloured crystalline syenite, 

 others close-grained pink felsitic rock. The matrix is a claret- 

 coloured earthy, homogeneous, felspathic paste, with here and there 

 a coarser or crystalline structure, or a few imperfect felspar crystals 

 and grains of quartz. The fragments are often quite rounded, like 

 shore pebbles. Following the band along its trend we find varia- 

 tions in the size of the fragments, and in the proportion of the 

 different kinds, but otherwise its general character prevails as far as 

 it is exposed. 



If, however, we trace this fragmental mass across its trend into the 

 adjoining part of the rock, we find that the fragments cease to be 

 round, and their sides are bounded by the continuation of the joints 

 which affect the whole rock. The claret-coloured matrix disappears, 

 being represented first by thin bands along the outside of the 

 angular fragments, then by mere lines of colour along the joints. 

 The pink felsitic fragments run together, and are at last seen 

 united in a vein (C D) of compact pink felspar-rock, such as is so 

 common in the Malvern Archaean. Where the vein has got much 

 broken up and displaced, we find sometimes, on the margin and at 



1 Geol. Mag. Vol. X. 1883, p. 306, " On the Brecciated Bed in the Dimetian of 

 St. Davids." 



