Page:The Geologist, volume 5.djvu/62

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3. Upper Lanarkshire coal measures:—Wholly fluviatile organic characters.

2. Beds of marine and fluvio-marine limestone intercalated with shale, coal, ironstone, and stratified trap.

1. Shales, sandstones.

3. Sandstones, shale, and a bed of coal.

2. Freshwater limestone.

1. Shale, sandstone, tufa.

On the Bathgate Hills the marine limestone is sixty feet thick, and the fluviatile limestone about twenty feet thick. But towards the south-west, on the borders of Edinburgh and Lanarkshires, the marine limestone thins into beds of from three to six feet thick, whilst the freshwater bed is above fifty feet thick.

The Torbane Hill bed lies in number two of the left-hand series of strata. Along with two or three local coal-seams, it occupies a small mineral basin some two or three miles in area, lying immediately above the mountain-limestone, but stratigraphically distinct from the upper Lanarkshire coal-measures. The petrological structure of the surrounding strata is very unique; let us try to evolve their history.

The physical changes closing the life-era of the Scottish old red sandstone system are difficult to determine. From various geological reasons, the chief of which are the wave-ripples on the sandstones, and the physical structure of the surrounding mountain-chains, it has been deduced that central Scotland was a strait or frith bounded as now by the prominent peaks of the northern and southern Highlands. Islets, covered by a strange vegetation, dotted this watery expanse; from the eastward strong currents brought down the spoils of a now lost land, depositing the shales and sandstones so predominant round the Scottish metropolis. In this quarter, too, an intense volcanic activity prevailed.

The trappean bosses, which form so prominent a feature in the landscape round Edinburgh, were mostly erupted at this time. So, at least, the labours of Mr. Geikie and others go to prove.

From St. Abb's Head to Bathgate a chain of volcanos sent up their lurid contents into the Carboniferous sky. Nowhere was this activity more intense than on the Bathgate hills. The freshwater series to the eastwards of our section are everywhere intercalated with trap; some of it developed as aerial ash-beds, the rest as submarine greenstones. The prominences round Winchburgh, Binny, and Linlithgow, which the railway-traveller may remember so boldly characterize the scenery, are the memorials of these eruptions. The spot pointed out as the axis of the hills was undoubtedly the vent of a very active volcano. Immediately above Bathgate four or five great beds of basaltic greenstone and ash lie so intercalated with the aqueous strata as to