196 



HARDWICKE'S SCTENCE-GOSSIP. 



arches of the Giffnock quarries rank among the 

 most interesting sights of Glasgow. 



The Carboniferous limestone series of the west 

 of Scotland is very rich in fossils. No limestone 

 need be searched in vain, and every blaes-heap is 

 full of organic remains. Perhaps, of all the lime- 

 stones, that of Broadstone, near Beith, has yielded 

 the greatest quantities. Its polished surfaces, fan- 

 tastically marked with encrinites, corals, and shells, 

 cut at every possible angle, form a " marble " once 

 in great request for ornamental purposes. In the 

 older houses of the better class, one lights every 

 now and then on a mantelpiece of this material, 

 which is quite a little museum of carboniferous 

 limestone fossils.* 



We are now coming upon rocks which are at 

 once more ancient and more distant from the city, 

 which we regard as our starting-point. Glasgow 

 stands geologically, as has already been remarked, 

 in the centre of a basin, and therefore the lower 

 formations may be reached, either by boring verti- 

 cally for a few thousands of feet, or by walking a 

 horizontal distance of a few miles. We could find 

 the base of the carboniferous limestone series by 

 sinking five thousand feet below Glasgow (the thick- 

 ness of the millstone grit and carboniferous lime- 

 stone), or by walking till we found the subjacent 

 beds rising to the surface. This they do at a dis- 

 tance varying from five to twelve miles. 



The formation thus reached is composed of alter- 

 nate beds of volcanic lavas and ashes, and builds up 

 the fine trappean ranges of Campsie, Kilpatrick, 

 and Renfrewshire. These lavas (porphyrites and 

 melaphyres) and ashes dip, as the Kilpatrick Hills, 

 under the carboniferous limestone series, re-emerge 

 and again disappear to the south of Glasgow as the 

 Cathkin Braes, and rise once more in the Muirland, 

 at the heads of the Avon and Irvine. A few sedi- 

 mentary beds, other than ashes, intervene between 

 the lava-flows in the Kilpatrick Hills. The whole 

 range is famous among mineralogists for beautiful 

 specimens of zeolites. The extreme fragility of 

 most of these minerals makes it desirable to resort 

 for specimens to newly-opened quarries. Some 

 characteristic specimens of Prehnite are, however, 

 still to be had in the rubbish excavated from the 

 Bishopton tunnel on the Greenock Railway. 



The base of the volcanic series may be seen rest- 

 ing on sedimentary rocks of Lower Carboniferous 

 age at Fintry, Strathblane.f Overton, near Bowling, 

 Ardrossan.J and the island of Little Cumbrae, in 

 the Firth of Clyde, as well as in Bute. On re- 

 emerging on the eastern side of the Lanarkshire 



* For lists of carboniferous limestone fossils see Armstrong, 

 Young, Craig, and others, in "Trans. Geol. Soc. Glasgow." 

 Also R. Etheridge. Jun., in Explanations of Sheets 14, 22, 

 and 23, Geological Survey. 



t See Geological Survey, Sheet 27, Stirling. 



t Ibid., Sheet 22, Scotland (1-inch). 



coalSeld as the Garlton Hills, the volcanic series is 

 found to have dwindled away to a fraction of its 

 thickness on the western side, while a great series 

 of sandstones, cement-stones, and shales, including 

 oil-shales, has largely taken its place. The mean- 

 ing of this is, that while the volcanos on the east 

 had ceased to be active, and the quiet deposition of 

 sediment (for the most part in lakes) was going on, 

 those on the west still vomited lavas and ashes. A 

 considerable thickness of cement-stones and shales 

 does indeed underlie the trappean series on the 

 west side— notably at Strathblane ; but the upper 

 portion of the series, containing the oil-shales of 

 Mid Calder, is not represented. 



By far the most interesting record still remaining 

 of the volcanic activity of this period, affording, as 

 they do, views of the internal structure of volcanos, 

 are the " necks " or " pipes," which along a line 

 from Ardrossan to Fintry, pierce the older rocks 

 where these emerge from beneath the bedded traps 

 and ashes. The necks are isolated dome-shaped 

 hills of coarse volcanic agglomerate, or of mela- 

 phyre, or both. They are not the original cones 

 from which the lavas and ashes were thrown out, 

 for these, of course, towered above the deposits, 

 which they spread around their bases, and have dis- 

 appeared bodily, their sites having been probably at 

 one time deeply buried under deposits of Car- 

 boniferous Limestone age. The necks then are the 

 plugged-up vents of the volcanos, originally deep- 

 seated, but now standing up boldly as hills, as they 

 have yielded more slowly to the wasting power of 

 denudation than the softer rocks through which 

 they pierce. Fine examples (especially the two 

 last-named), are Diamond Hill, near Fairlie ; Knock 

 Hill, near Largs; Dumbarton Castle Rock; Dum- 

 buck, near Bowling ; and Dumgoyn, in Strathblane. 



Still receding from Glasgow westward, the red 

 sandstones appear, which form the lower sub- 

 division of the calciferous sandstone series. They 

 extend over Dumbarton Muir, and the eastern 

 shore of the Firth of Clyde, from Greenock to 

 Ardrossan. They also bulk largely in the composi- 

 tion of Bute and the Cumbraes. They are supposed 

 to be lake-deposits, and, at least in the neighbourhood 

 of Glasgow, are almost destitute of fossils, even the 

 cornstones and limestones of the series having been 

 searched in vain. Elsewhere, these sandstones are 

 called Upper Old Red. They lie on the lower old 

 red sandstone, unconformably, that is to say, the 

 deposition of the lower old red sandstone ceased in 

 the area in question, the lake-bottom became dry 

 land, and the rocks deposited in the lake-bottom 

 suffered atmospheric denudation before another 

 depression admitted of the superposition of the 

 upper old red sandstones. 



The lower old red sandstone may be seen in the 

 course of a day's excursion around Glasgow, 

 although the unravelling of its structure may be 



