CHAP. XXVI II 
PUYS OF THE FIRTH OF FORTH 
465 
Imond. We shall probably be witbiii the mark if we set clown the original 
area over which puys broke out and spread abroad their lavas and tuffs as 
covering about 300 square miles of the lagoons and jungles of Central 
have already shown that the range in geological time of the puy- 
eruptions in this district extends from a low horizon among the Calciferous 
..aiidstones through the Carboniferous Limestone series, up to nearly the 
evel of the Cahny Limestone, which lies not far from the top of that series, 
ihe vertical thickness of strata between these two stratigraphical limits, when 
lere are no intercalated volcanic rocks, is probably more than 4000 feet. 
Ihe vents from which the volcanic materials were ejected, so far as they 
are now to be observed at the surlace, may be divided into two groups, one 
ying to the north, the other to the south of the Lirth of Forth. The 
northern or Fife group may he followed over an area 15 miles loim and 
about three miles broad. Some fifteen separate vents may be recognized in 
It, distributed chiefly at the two ends of the belt, a cluster of about six risino- 
around Burntisland, while another of nearly as many appears at Saline. The 
characters of some of these necks have been already given in the forecroiim 
pages. “ ® 
The southern or West Lothian group includes alioiit a dozen vents which 
are scattered over an area of some 60 square miles, extending from the 
coast-hne between Borrowstounness and Queensferry southwards to Batho-ate 
and Uphall. In this group Biiiiis Hill, a mile long by almost half a mile 
broad, and r using to a height of nearly 300 feet above the sea, forms the 
most prominent individual. But the vents are generally smaller in the 
southern than in the northern group. 
The manner in which the vents have been left filled with volcanic 
material has been described in previous pages. Jlost of them are occupied 
by tuff or agglomerate. In many cases the neck consists entirely of pyro- 
clastic detritus, as in most of the vents of eastern Linlithgovvshire and iiiany ■ 
of those in Fife. Hot infrequently a column of basalt has risen in the 
funnel and solidified there, as exemplified by Biiiiis Hill and Saline Hill 
or the basalt has filled rents in the tuff and now appears in dykes like those 
on the Binn of Biirntisland (Figs. 148, 14t), 159, 1G6, 168)' 
But It IS possible that in some cases vents maj- be represented by bosses 
Of basalt or dolerite, unaccompanied by any agglomerate or tuff. Perhaps 
the best example of this suggested origin is supplied by Galabraes Hill, which 
nses through the Hurlet Limestone and the volcanic series of the Batlumte 
Hills, about a mile north-east from the town of Bathgate. This eminence 
rises to a height of 940 feet above the sea, and consists of a rudely elliptical 
boss of basalt, measuring .3500 feet in its greater and 3000 feet in its minor 
axis It disrupts the sedimentary and volcanic series, which can be traced 
up to It on all sides. Some of the smaller circular or elliptical bosses in 
eastern Linlithgowshire and western Fife may perhaps belong to the same 
category. But undoubtedly most of the intriisii'e basalts and dolerites of 
this volcanic region are sills. 
