Jotne Strata in Ireland and Scotland. pi 
About two hundred yards north from Freeport Lodge is a 
Whyn Dyke, which ranges N.W. andS.B.,and appears in that 
direction on the Jura fhore, which is more than a mile did: ant. 
Th is Whyn Dyke is bare at the cliffs feveral yards in height, 
and is near nine feet in width. It confifts of an inner part of* 
a granular and fomewhat porous texture, of a dark grey co- 
lour, with flbining parts like mica, includes opaque zeolite 
fpecks, and its fpecific gravity is 2,81 1. On each fide of this, 
and divided from it by fiiiall vertical fuTures or joints, not more 
than an eighth, or at the moft a quarter, of an inch wide, are 
two bodies, each near eighteen inches in width, of a dark co- 
lour, much refembling the preceding fubftance, but without 
the zeolite fpecks; the fpecific gravity is 2,850. Both the 
outer and inner fubftances (lightly effervefce with the nitrous 
acid; both are magnetic, and both give fire with fteeh The 
whole mafs is interfered, at various diftances, by lateral joints, 
and is included between the chert rock, which does not appear 
the lead altered where it comes in contaQ: with the Whyn 
Dyke. Farther along the fhore is a cavern in the chert; the 
entrance is low and narrow, but within it is very capacious. 
Intending to vifit the cave Ea mawr, on the weftern fide of 
the ifland, I took boat at Freeport, and rowing along fhore, 
which is of chert, I obferved feveral fiffures or caverns in the 
cliffs, and many Whyn Dykes, lome ranging N.W., others N.E. 
I landed, within the found, on a white fhingly beach, the ftones 
of which are all chert, rounded by attrition, and the fhingle is 
thrown up fo much above the prefent high-water mark, that 
it affords ftrong reafon to believe, that the fea has greatly re- 
ceded from thefe fhores. Above the beach, the cliffs are of 
chert. From hence I walked three miles over moors and open 
paftures acrofs the north- weft point of the ifland, and in fome 
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