504 Proceedings of the Royal Irish Academy. 
of Wicklow and Dublin, by J. Beete Jukes, M.A., P. U.S., and G. V. 
DulSToyer, M.E.I. A., published in 1869 (subsequent to the deaths of 
these gentlemen), and in the section describing the Bray Head district, 
at p. 25, occurs the paragraph : — The southern end of the coast sec- 
tion affords the usual greenish and reddish purple grits and hard slate 
layers ; and at a distance of about half a mile E". of the Cable Rock (or 
Half -tide rock) these are traversed somewhat in their line of strike, i.e. 
from JST.E. to S.W., by a greenstone dyke which on the shore branches 
into numerous veins. The N'.E. end of the dyke is dislocated for the 
distance of about 60 yards by a fault neaily E. and W., the down 
throw being to the south. The dyke can be traced up the hill for the 
distance of about 260 yards." The following foot-note is added : — 
This dyke was first discovered by Professor Harkness, and has been 
minutely described by Mr. "W. H. S. Westropp in the Journal of the 
Geological Society of Ireland for the year 1866." 
Turning to this description, which appears in vol. i., part ii., for 
the year 1865-66, p. 149, with the title, "On a Trap Eock at Bray 
Head, Co. Wicklow, by W. H. Stackpoole "Westropp, M.E.I.A.," the 
following details are therein found : — 
P. 150. — " Some time ago Professors Harkness and King discovered 
a bed of greenstone about 100 yards south of the Windgate quartz rock, 
by the side of an old road, running a little above the present walk, 
which skirts the eastern side of the hill ; these gentlemen told Mr. 
Jukes of its occurrence there, and during Easter week last year (1864) 
Mr. Jukes showed it to me when he was giving a field lecture to his 
Geological Class ; he said he had traced it up the hill, but that no one 
had tried to find its extension down to the seashore." 
The author then gives the following results of his examination : — 
" Erom the place where the trap can be first seen towards the top of 
the hill, down to the spot where Professors Harkness and King noticed 
it by the old roadside, it appears to occur in one bed about 5 feet thick, 
regularly interstratified with the grits and slates. In the cliff between 
the walk and the railway it begins to show a tendency to split up, for 
a second bed only an inch or two thick appears, which runs parallel to 
the mainbed, and is separated from it by grits, &c. The trap disap- 
pears under the railway embankment, and would not again be seen 
but for a fault having an upthrow to iT.K.W. of about 150 feet; this 
brings up the trap about 60 yards to the jN"., where it may be seen on 
both sides of the railway near the south entrance of the tunnel. 
Below the railway it becomes split up into several beds ; and on the 
eashore I counted as many as seven, varying in thickness from 
