CHAP. XXVI CHARACTER AND DISTRIBUTION OF THE PUYS 
415 
formation that the eruptions which produced them reached their greatest 
vigour and widest extent. Here and there in Scotland evidence may he 
found that the phase of the Puys began during that earlier section of 
Carboniferous time recorded by the Calciferous Sandstones. This is 
markedly .the case in Liddesdale and the neighbouring territory. Over 
the western part of Midlothian also, the eastern portion of West Lothian, 
and the southern margin of Life, abiindant traces occur of puy-eru})tions 
during the deposition of the Calciferous Sandstones. Elsewhere in Central 
Scotland there is no evidence of the vents having been opened until after 
the deposition of the Hurlet Limestone, wliich, as we have seen, may con- 
veniently be taken as the base of the Scottish Carboniferous Limestone 
series. The volcanoes remained active in West Lothian until near the close 
of the time represented by that seiies ; but in Ayrshire they continued in 
eruption until the beginning of the accumulation of the Coal-measures. 
These western examples of the puy-type are, so far as I am aware, the 
latest known in Britain. 
Whether or not the earliest puy- eruptions began before the latest 
plateau-lavas and tuffs were accumulated is a question that cannot be readily 
answered. It will be remembered that in the basin of the Eirth of Forth 
a thickness of more than 3000 feet of sedimentary strata, including the 
Burdiehouse Limestone and numerous oil-shales as well as thin coal-seams, 
lies above the red and green marls, shales, sandstones and cement-stones of 
the Calciferous Sandstone series. This remarkable assemblage of strata is 
absent in the western parts of the country, where the top of the Clyde 
volcanic plateau is almost immediately overlain by the Hurlet Limestone. 
If we were to judge of the sequence of events merely from the stratigraphy, 
as expressed in such sections as Figs. 137, 138, 139 and 140, we might 
naturally infer that as no trace of any break occurs at the top of the Clyde 
plateau, the tuffs .shading upward there into the limestone series, no 
important iiause in sedimentation took place, but that the last volcanic 
eruptions were soon succeeded by the conditions that led to the deposition 
of the widespread encrinite-limestones. If this inference were well founded 
it would follow that while the plateau-eruptions in the west lasted till the 
time of the Hurlet Limestone, those in the east ceased long before that time 
and were succeeded by the puys of Fife and the Lothians. There would 
thus be an overlap of the two phases of volcanic action. 
I am inclined to believe, however, that in spite of the superposition 
of the Hurlet Limestone almost immediately upon the volcanic rocks of 
the Clyde plateau, and the absence of any trace of a break in the process of 
sedimentation, a long interval nevertheless elapsed between the last erup- 
tions and the deposit of that limestone. The Campsie section (Fig. 140) 
shows us how rapidly a thick mass of strata can come in along that horizon. 
The volcanic ridges may have remained partly unsubmerged for such time 
as was required for the subsidence of the Forth basin and the deposit of the 
thick Calciferous Sandstone series there, and their summits may only have 
finally sunk under the sea not long before the Hurlet Limestone grew as a 
