560 Notices of Memoirs — Prof. E. JELuU — Irish Boulders. 



fully would require a plan and sectional elevation ; but so mucli ha& 

 already been laid before the geological public with regard to this- 

 particular junction that I refrain from the infliction. 



The Cambrian rocks to the south of this junction strike across the 

 harbour of Porth-clais nearly due east and west, and on the left or 

 east bank the granite is directly in contact with the green Cambrian 

 shales. The conglomerate is not to be seen. At a distance of about 

 30 feet north of this contact, and embedded in the granite, is a vein ^ of 

 green shale about 18 inches across, and another about 10 feet nearer 

 to the contact about 6 inches across. Both these veins of shale, but 

 especially the thinner one, have a rudely columnar structure at right 

 angles to their direction. Excepting that this shale is a little more 

 indurated and more like slate in its constitution, it is similar to the 

 Cambrian green shales that overlie the basal conglomerate. These 

 veins are in my view undoubtedly part of the Cambrian shale 

 entangled in the granite, so that the granite must be post-Cambrian. 



I cannot see any way of escaping from this conclusion. I may 

 add that the conglomerate in contact with the granite, as befor© 

 described on the opposite side of the valley, is converted into an 

 extraordinarily tough rock. Though I saw no veins of granite 

 penetrating the adjoining rock, I have little difficulty in recognizing 

 these alterations as ordinary contact phenomena. 



In the face of this strong evidence to the contrary, it appears to 

 me that the presence of " dirty quartz " in the conglomerate like 

 that in the granite, a resemblance that may be accidental or fanciful, 

 but is much insisted upon by Dr. Hicks, has no great weight in 

 proving that the conglomerate is largely made up of materials from 

 the granite, and that therefore the granite is pre-Cambrian. 



I. — Note on a few of the many remaekable Boulder- stones 



TO BE FOUND ALONG THE EASTERN MaRGIN OF THE WiCKLOW 



Mountains. By Professor Edward Hull, LL.D., E.E.S., 

 Director of the Geological Survey of Ireland.- 



AMONGST the evidences of the former existence of an extensive 

 sheet of ice descending from the Wicklow Mountains towards 

 the shores of the Irish Sea is the occurrence of boulder-stones, 

 chiefly formed of granite or granitoid gneiss, derived from the 

 mountainous range to the westward, of a size seldom equalled 

 — probably not surpassed — amongst the British Isles. As the 

 Association includes in its labours the task of collecting details 

 regarding erratic blocks, it may prove of interest, if I record a few 

 cases which, have come under my own notice. 



1. The Motilia Stone.— This, remarkable boulder is perched on 

 the summit of Cronhane Hill, above Castle Howard, and is a 

 conspicuous object from all directions. It consists of grey granite, 



1 1 use the terra ' ' vem " because it best describes the form in which these remnants 

 of the shale occur. 



2 Eead before Section C. (Geology), British Association, Manchester, Sept. 1887. 



