﻿256 ME. C. I. GAEDINEE AND PEOF. S. H. EEYNOLDS ON [May 1 0. 1 0, 



Miss Elles considers that this assemblage proves that these beds 

 belong to the upper part of the zone of Didymograptus ecctensus. 

 In our previous paper x we quoted Miss Elles as assigning the grapto- 

 litic fauna of the Treanlaur stream near Tourmakeady to about 

 the Didymograptus-hirundo horizon, that is, to a slightly higher 

 horizon than that of the Lettereeneen beds. Stratigraphical con- 

 siderations, however, render it very probable that the two sets of 

 beds are approximately on the same horizon, and Miss Elles informs 

 us that the fossil evidence is not inimical to this view ; she further 

 points out that the Didymograptus bijldus which is abundant at 

 both these localities is a small and early mutation of the form 

 characteristic of the bifidus zone proper. 



In addition to the main outcrop of these beds, Bands 4 & 3 and 

 part of Band 2 are repeated by a strike-fault running close to the 

 top of the ridge on its northern side. But, although fragments of 

 black chert litter the ground along the line where Band 3 occurs, 

 no actual exposures are here seen, either of the chert or of the grapto- 

 litic beds. 



The coarse tuff or breccia in Band 3 is a noteworthy rock. The 

 fragments, which sometimes have a length of about 2 inches, show 

 r.a pure white on a weathered surface, and the contrast between 

 this and the black matrix in which they are embedded renders the 

 Tock very conspicuous. Under the microscope, the fragments are 

 seen to consist of quartz-felsite and the matrix to be very felspathic 

 and quartzose. 



Sections of cherts and fine, more or less silicified tuffs, from 

 several points along the line of outcrop of Band 3, disclosed the 

 presence of radiolaria similar to those described by us from the 

 Tourmakeady district. 



(2) On the southern slopes of Greenaun Hill. — This 

 •area, which has a visible length of about a third of a mile, is 

 almost continuous with that just described. It is bounded by 

 faults on all sides, except on the southern one, where it is covered 

 up by peat and drift. The rocks are finely exposed in certain 

 •cuttings due to the making of the new road from Cappaghduff West 

 to Barnahowna. The most noteworthy feature of these exposures 

 is the extraordinary amount of disturbance which the rocks show, 

 the chert bands being puckered and disrupted in a manner that 

 can be better illustrated by photographs (see fig. 1, p. 257) than 

 by descriptions. 



All the rock-types described as occurring in the district farther 

 to the west can be noted here, and the intimate association of the 

 cherts and tuffs is very well seen, the cherts clearly owing their 

 origin to the silicifi cation of beds of very fine tuff. The chert bands 

 reach a considerable thickness, one being at least 3J feet thick ; 

 but it is possible that, in some cases, the apparent thickness may be 

 due to the crumpling together of several bands and the squeezing 

 out of intervening beds. No graptolites were found in this area. 



1 Quart. Journ. Geol. Soc. vol. lxv (1909) p. 108. 



