CHAP. XXVII 
LAVA-STREAMS AND TUFFS OF THE PUTS 
443 
a sill. An instance of its development in an undoubted .sill will be 
described fnrtlier on. ^Nevertheless, if we follow the trend ol the olccinic 
baud of the Bathgate Hills southward for only two miles beyond the picrite 
quarry, we find in the Skolie Burn a rock in many res])ects' similar, and 
quarried for the same ]iurpose of building oven-soles. This “ leckstone ” is 
Fig. 154. — Section of the upper surface of a diabase (“leckstone”) sheet, Skolie Burn, south-east 
of Bathgate. 
blue c.alcarcous shales ami thin limestones. 
there seen to be surmounted by a group of calcareous shales and thin 
limestones. The section laid bare in the stream is represented in Fig. 1 o ^ . 
Immediately above the diabase, which is highly cellular, lies a green felspathic 
sandstone or shale containing detached fragments of the amygdaloid toget lei 
with Liurjvlm and otlier shells. There seems no reason to doubt that tins 
is a true interstratified lava.^ 
Where the piiys attained their greatest development in Scotland, they 
rose ill the shallow lagoons, and here and there from deeper parts of the 
sea-bottom, until by their successive discharges of lavas and tufts they 
Gradually built up piles of material, whicli, in the Linlithgow and Jiathgate 
district, may have 1 )eeii nearly 2000 feet in thickness. It must 1 )e remembered, 
however, that the eruptions took place in a subsiding area, and that even the 
thickest volcanic ejections, if the downward movement kept pace with the 
volcanic activity, need not have grown into a lofty volcanic hill. ^ Indeed 
largely as the lavas and tuffs bmlk in the geology of some parts of Centra 
Scotland, tlieir eruption does not seem to have seriously interfered witli the 
broader physical changes that were in progress over the whole region. Thus 
the subsidence wliicli led to the spread of a marine and limestone -making 
fauna over much of Central Scotland included also the volcanic districts. 
The limestones, formed of criiioids, corals and other marine organisms, 
extended over the submerged lavas and tufls, and were even interstratified 
with them. 
While the volcanic materials are found to replace locally the ordinary 
Carboniferous sedimentary strata, it is interesting in this regard to note 
that, during pauses in the volcanic actiidty, while the subsidence doubtless 
was ’still going on. some groups of sandstones, shales or limestones extended 
themselves across the volcanic ridges so as to interpose, on more than one 
1 Trans. Roy. Soc. Min. xxix. (1879), pp. 503-507. 
