fame Strata in Ireland and Scotland. 
u / j 
Dykes is near twelve feet in breadth, and ranges N. by E. and 
S. by W. Your fubfeqnent voyage to Raghery difcovered 
that the Whyn Dykes pervade that ifland. 
Returning to Dublin, through Clogh, Ballymena, Antrim, 
Glanevy, Moira, Ban bridge, Loughbrickland, and until within 
a (hort di dance of Newry, I conftantly faw tumblers of lava, 
and income places the fixed mafs of lava, in which were fif- 
lures ranging N.E. and S.W. 
When I reached home, my mind being ftrongly imprefled 
with the fimilitude that fubfifts between the Hay Whyn Dykes 
and thofe of Ballycaftle, which take their rife in a country 
•/ 
confefledly abounding with volcanic matter ; that I might be 
enabled to form a better judgement of their fubftance when I 
Ihould again vifit Hay, I repeatedly and attentively examined 
the Derbyshire toadftone in the neighbourhood of Buxton, and 
found it very like the fpecimens of the Whyn Dykes, which 
I had brought with me from Hay. 
Early in the laft fummer I went into Ireland, and having 
fpent fome time at the mines in the county of Wicklow I 
proceeded to Belfaft ; and a little to the northward of that 
town (near the fpot where an unluccefsful trial was fome time 
fince made for coal), I difcovered in a bank a body of marl, 
running N.E. and S.W, between red and white fand-ftone, the 
whole included and furmounted by a kind of toadftone and 
rude lava, whofe joints had no particular direction. Above 
five miles north from the town, is a mountain called Cave 
Hill (from its containing three natural caverns) ; at the diftance 
from which I faw it, the fummit appeared bafaltic, under 
which is white limeftone. 
At Belfaft I embarked for Ilay; but the wind, hanging 
to the northward, obliged us to tide along the Irifh fhore, 
L 2 ' which, 
