678 ME. C. A. MATLEY ON THE [Aug. 1 899, 



rule the coarser rocks form fragments in the finer, but not infre- 

 quently ' pebbles ' (authiclasts) and matrix are made of the same 

 material. Many of the larger fragments have undergone no 

 mechanical deformation in their interior, but the smaller fragments 

 are kneaded and crushed, and the isolated grains of quartz are granu- 

 lated. Usually the fragments consist of a single type of rock, but 

 often several distinct types occur together. In the example (N.A. 

 63) from the vs^est side of Forth y Wylfa various grits, sericitic and 

 chloritic schists, etc., occur in a single rock-slide, as is the case v^ith 

 the thrust-conglomerates described by Gardiner & Reynolds from 

 Portraine.^ Sometimes quartzites of the * quartz-knob' type occur 

 in the conglomerates, but so far no fragments of volcanic rock have 

 been found in them ; indeed, in all the rocks examined there is 

 very little volcanic material. Quartzite-bands found in the crush- 

 conglomerates are much crushed. 



Discussion. 



The Rev. J. F. Blake said that the first impression created on 

 him by the paper just read was a sense of his own rashness eleven 

 years ago in attempting to explain the whole of the Monian system 

 in a single evening, whereas the Author that night had been unable 

 to conclude his account of even a very small portion of the rocks. 

 The second impression was one of satisfaction that an independent 

 worker, who had been enabled to devote some time to the subject, 

 practically confirmed all the speaker's contentions (quartz-knobs 

 excepted) ; which was all the more important, inasmuch as in the 

 new Index-map of the Geological Survey all the Monian rocks of 

 the district had been changed into Ordovician on the strength of 

 some supposed intercalations of black shale, which the Author now 

 rightly interpreted as a result of complex thrusting. He begged 

 that the Author would modify the statement he had made that the 

 speaker had claimed Orthis Bailyana as a Monian fossil. He had 

 never come nearer to that than saying tbat he should like to do so ; 

 but, after an examination of the Wexford beds in situ and the col- 

 lection in the hands of the Irish Geological Survey, he could find no 

 encouragement for any such idea. He quite appreciated the statement 

 of Prof. Watts that the northern so-called ' volcanic series ' did not 

 contain any fragments of volcanic rocks, or very few, in the shape 

 of lapilli ; but the angular scattered fragments of felspars, etc. 

 seemed to suggest some volcanic origin. He did not understand 

 the Author's section [fig. 9, p. 660], as the folds were indicated as 

 having a north-and-south axis, whereas, the pressure being from the 

 north, the axis must be east-and-west. 



With regard to the quartz-knobs, the best was seen near Parys 

 Mountain. Not every quartzite in the district was a quartz-knob, 

 and the rounded grains in many of the latter had been recognized 



1 Quart. Journ. Geol. Soc. vol. Hii (18'J7) p. 627. 



