112 Proceedings of the Royal Irish Academy. 



ciated with bedded and intrusive masses of hornUende-roch. Of such 

 rocks Jnkes says : " It is very possible that many hornblende-schists, 

 actinolite-schists, &c., are metamoi-phosed tnflts."*' Of tnif s and tuif ose 

 rocks Forbes thus "writes — " Subaerial or subaqneons ontbnxsts may 

 force into the sea irrnptive rocks, which, being at once broken np into 

 a state of division, more or less fine in proportion to the greater or 

 lesser cooling power of the water-mass in immediate contact, may be 

 spread ont into beds by the action of the waves. The texture of these 

 rocks may vary from that of the coarsest breccia down to the finest 

 mud, and, as is usually the case, such deposits may present themselves 

 as alternating beds of coarse and fine character. Upon the consolida- 

 tion of such formations, rocks are formed identical in chemical and 

 mineralogical composition with the original ii'iiiptive rock from which 

 they were derived, and wliich, particularly when close-grained, often 

 present an external appearance so like the original rocks as to be fi-e- 

 quently undistinguishable from them by the naked eye."f Scrope and 

 the other historians of the volcanic regions mention the accumulations 

 of agglomerates and other tutfose rocks often associated with volcanic- 

 rocks, while in various places in Ireland, such as the plain of Limerick 

 and the vicinity of Valencia Harbour, Kerry, there are similar accumu- 

 lations associated with plutonic rocks ; therefore, it does not appear at 

 all improbable that these ancient exotic rocks of Yar-Connaught should 

 also have had associated tuffs and other such mechanical accompani- 

 ments. 



The homblendytes of Tar-Connaught range from a fine, almost 

 compact, rock to a massive conglomeritic rock containing enclosed 

 masses or blocks often yards in width. 



The conglomeritic-homblendyte is always more or less associated 

 with protiTisions or beds of hornblende-rock. In places they gTaduate 

 into one another tlirough a nodular or spheroidal variety of the latter, 

 while the congiomeritic-rocks, on the other hand, gradually loose all their 

 blocks and merge into ordinary scliist. In others, the hornblende-rocks 

 and the conglomeritic are inteiTningled together iiTegularly, and the 

 mass formed of both combined, will be surrounded by the regular 

 stratified rocks of the country. Tins would seem to be additional 

 proof if any more is wanted, of these rocks originally being tuS. and 

 agglomerates; for such a mass as that represented in figs. Q, PI. 11, 

 and R, PL 12, may well be considered the remains of an accumulation 

 foiTued around a subaqiieous plutonic vent. 



In the immediate vicinity of a mass or tract of hornblende-rock the 

 enclosed blocks in the conglomerate will be, for the most part, some 

 one or other variety of igneous rock, some having an aspect like 

 scoria or pomice. Farther away they will be mixed with blocks of one 

 or more other kinds of rock, and eventually all the blocks will gradually 

 disappear and the rock graduate into an ordinary scliist. In one locality 



* Manual of Geology by J. Beete Jukes, M. A., F. R. S., second edition p. 82. 

 t The Microscojye in Geology, p. 10. 



