, • Mr. Mills’s Obfervations on 
ftone Tides, hading to the weftward. South-fouth. weft from 
hence is a natural cavity in the limeftone, called the Giant s 
Hole. Here the joints of the limeftone range S.E. and NAV . 
and are croffed by a (hale firing, three feet wide ranging N. ' • 
and S.W. The water of a little ftream, which tails into the 
Giant’s Hole, paffes through a fiffure in the limeftone, and 
ifi'ues again to the day in lower ground, fifty yards to the 
fouth-eaftward. Returned by Perfabus to Freeport, having 
gone over feveral Whyn Dykes of various widths, and run- 
ningr in various directions. 
From Freeport went (by Perfabus) to Gartnefs lead mine 
which is fituated in the center of the limeftone country ; muc i 
work has been done here, but at prefent there are no great 
profpefts of fuccefs. The principal vein, which in tome pairs 
is about one foot wide, has a flight hade to the north-eaftward, 
and ranges fouth-eaft and north-weft, along the fide of an 
immenfe Whyn Dyke, between which and the hmettone it is 
included, the points of the latter running north-eaft and fouth- 
weft at right-angles with the vein and Whyn Dyke. _ 
This Whyn Dyke is the largeft I have yet feen, being 
twenty-three yards wide. Where cut through, from Abel s to 
HodefonV fhafts, it divides the limeftone ftrata, and is near y 
vertical, having, like the vein, a very flight hade to the nort i- 
eaftward. It is chiefly compaft, but not entirely without 
fiflures. It varies both in colour and texture ; in fome part, 
approaching to the texture and hardnefs of bafaltes ; m ot «rs, 
b eL granular, of a black iron-grey colour with fhming pan., 
givef fire with fteel, is flightly magnetic, does not effervefee 
with nitrous acid, and its fpecific gravity is 2,631, O he 
parts, of nearly the fame texture and colour, have none 
of the preceding qualities; fpecific grayity 2,69b. Some 
2 
