IGNEOUS GEOLOGY OF THE BATHGATE AND LINLITHGOW HILLS. 363 
the effect of the Haugh Burn fault. Petrographically, the zone is composed of a 
number of alternating bands of olivine-basalts and olivine-dolerites. Transverse 
traverses in the neighbourhood of Clarendon, Hiltly, Wairdlaw, or Hilderston readily 
reveal this structure. As a rule, however, these bands cannot be traced far in a north 
and south direction. A stratified intercalation of ash and ashy shales is found in 
Preston Glen, and another of limestone and shales at Wairdlaw. The basalt overlying 
this limestone is noteworthy, both for its platy jointing and for the fact that it is 
the only lava throughout the whole volcanic series which contaims phenocrysts of 
felspar in any abundance. The same rock can be traced on the south side of the 
valley at Wairdlaw, but the limestone below is nowhere visible. A line of springs 
behind Craigmailing probably marks the prolongation to the south of this sedimentary 
intercalation, and indications of its presence are also found on the eastern slope of 
Cathlaw Hill. Towards the south interbedded sediments probably become more 
abundant. Two bands are exposed in the Mavis Glen, and these can be traced for a 
considerable distance to the north and to the south by means of the shallow depressions 
between the lavas to which they give rise. 
The lavas of this zone cannot be traced to the north of Linlithgow Loch. In all 
probability they rapidly run out, and their place appears to be taken in part by a 
thick bed of voleanic ash found in a bore in Bonnytoun farm. Farther north the 
sandstones, shales, and thin limestones of Carriden probably occupy approximately the 
same horizon. 
The Index Inmestone and the Bo'ness Lavas. 
Between the fourth and fifth volcanic zones there occurs in the Bathgate Hills an 
important belt of sedimentary rock, which includes the lower Bathgate coals and the 
Index limestone. It retains a fairly uniform thickness and character from Bathgate 
to Kipps. North of Kipps, however, the thickness. gradually increases, and volcanic 
material becomes mingled with the sedimentary. On the eastern slope of Cockleroy a 
bed of ash appears not far below the probable position of the Index limestone, and at 
Kettlestoun fine-grained volcanic mudstones, passing into ashy sandstones and shales, 
are found overlying the lavas of the fourth volcanic zone. Between Kettlestoun and 
Linlithgow Bridge the only exposure is in the river Avon at the railway viaduct, where 
a very vesicular basalt lies a few feet below the Index limestone. The journals of 
bores quoted by Mr Cape u seem to indicate that a considerable proportion of the rock 
below the glacial gravels of this district is of volcanic origin. This change in the 
character of the strata makes it very doubtful whether the Kipps coals and the Index 
limestone are continued across Cockleroy to Kettlestoun. It is quite possible, however, 
that the coals do exist, but almost certainly in an attenuated form, of no commercial 
value, and much destroyed by intrusive rock. 
North of the Edinburgh and Glasgow Railway the Index limestone is repeatedly 
exposed in the river Avon, while the sedimentary zone, as a whole, opens out rapidly 
