578 Mr. J. Beete Jukes and the Eev. Samuel Haughton on the 



Head and Tara Hill, as the highestbedsof the district; and we should conclude 

 that these highest beds were those (so remarkably free from igneous rocks of 

 all kinds) which strike N. E. and S. W. from near Arklow Head to near New 

 Ross. 



The results agree, too, in placing the contemporaneous traps, as a mass, in an 

 intermediate position between these upper beds, and a lower set, the base of 

 which reposes, whether unconformably or in apparent or real conformity, on 

 the Cambrian rocks. 



Another point in which they agree, also, is the number of small el van dykes, 

 which, both in Wicklow and Wexford, are found in these lower beds, intru- 

 sive into, altering, and slightly cutting across them, although always agreeing 

 very nearly with them in general strike. 



There is, however, now one curious discrepancy to be alluded to. If we 

 suppose that the black slates of the Cambro-Silurian series, which rest directly 

 on the Cambrian rocks, are always the lower part of that series (and we have 

 no reason to make any other supposition), it then follows that the slates which 

 lie between Eathdrum and Wicklow on the one hand, and Rathdrum, Glen- 

 dalough, Roundwood, and Powerscourt, on the other, are the lower part of the 

 Cambro-Silurian series, the part below the trap beds. These are the beds 

 which in North Wicklow, from Glendalough to Killiney, are penetrated by the 

 granite. We saw reason, however, just now, for supposing that the beds 

 penetrated by the granite in Wexford were the beds above the traps. We 

 ou"ht, therefore, in walking along the margin of the granite from the one 

 part of this district to the other, to come to some locality where the bedded 

 traps themselves range up to the granite, and are equally cut through by it. 

 The felstones of the neighbourhood of Rathdrum and Ovoca, striking from 

 the N. E. to the S. W., ought, if they are continued, to range up to the granite 

 somewhere about Tinahely. No such trappean group, however, is anywhere 

 met with on the flanks of the main granite area F. 



Looking at the persistency of the trappean group through Waterford and 

 Wexford, everywhere dipping on the whole to the north-west, and at the reap- 

 pearance of this group in part of Wicklow as the beds rise again in that direc- 

 tion and dip to the south-east, we can hardly avoid coming to the conclusion 

 that before the rocks were disturbed, and while they remained horizontal, there 

 was a continuous trappean group, with a thickness of two or three thousand feet, 



1 



