194 



HARDWICKE'S SCIENCE-GOS SIP. 



On the outskirts of Glasgow, especially to the 

 west and south, a stranger will be struck by the 

 number of smooth-backed hills, shaped like eggs, 

 lying on their sides, and half- buried. These 

 hills rise to the height of one or two hundred feet. 

 They are the drums or drumlins of Celtic geolo- 

 gists, and are formed of boulder clay, resulting from 

 the passage of great sheets of ice. Sauchiehall- 

 street lies between two drums. On the occasion 

 of the last meeting of the British Association in 

 Glasgow, the late Professor Agassiz found in one 

 of these drums, then laid bare for building opera- 

 tions, the key to the geology of the Ice age. Similar 

 sections will be found at present where new streets 

 are rising on the sides of the Great Western road . 



The drums form the shores of, or islands in, an 

 immense deposit of stratified fine mud and clay, 

 which rises to a height of 100 feet above the sea. 

 It contains great quantities of marine and estuarine 

 shells, frequently of species now living only in 

 Arctic seas. This interglacial sea corresponded in 

 extent with the triangular flat which may be 

 called the Paisley basin, and which is, roughly 

 speaking, bounded on the -south by the Johnstone 

 Canal, on the west by a line from Johnstone north- 

 ward to Bishopton, and on the north-east by a Hue 

 parallel to and about a mile north of the Clyde, 

 between Old Kilpatrick and Partick. It must have 

 communicated with the ocean by one or perhaps by 

 two straits, the one at Kilburnie and the other at 

 Erskine Ferry. It has been suggested, with some 

 probability, that glaciers may from time to time 

 have pushed down the Loch Lomond valley, and so 

 dammed up the northern or present outlet of the 

 inland sea. In that case the sole outlet for the 

 inland sea, fed by all the drainage of the Upper 

 Clyde, would be down the valley of the Garnock to 

 Irvine. The bottom of the clay deposits is in many 

 places below the present sea-level, so that the 

 inland sea filled up a rock basin nearly forty square 

 miles in extent. 



The clay deposits of the Paisley basin rest, as has 

 been indicated, on boulder clay. Their interglacial 

 character is settled not less by their fossil contents 

 than by the direct superposition {teste llev. Win, 

 Eraser and others), at Paisley and elsewhere, of a 

 true boulder chiy. It is not surprising, considering 

 their date and their nature, that they have suffered 

 much denudation during and since the gradual 

 uplifting of the laud. Several pauses in the eleva- 

 tion lasted long enough to admit of the erosion of 

 marine terraces, notably one at 50 feet above the 

 present sea-level, and local hollows have been filled 

 up with post-glacial sea-deposits, which it is a 

 matter of the greatest difficulty to separate from 

 the interglacial, as they occur in the same flat and 

 at the same level, and are made up of precisely 

 similar material. Besides the marine deposits, the 

 Clyde and the Black and White Cart have covered 



large portions of the flats with their alluvia. To 

 the north of the Glasgow and South- Western Rail- 

 way, from Ibrox Station to Johnstone, a succession 

 of clay-pits for brick and tile manufacture affords 

 an inexhaustible field for collectors of glacial 

 and post-glacial shells. Many valuable papers and 

 lists by Messrs. Geikie, Crosskey, Robertson, Young, 

 Burns, Bennie, Coutts, and others, will be found 

 in the " Transactions of the Glasgow Geological 

 Society." Some of the members of the society 

 possess unequalled collections of glacial shells. 



Ofkaims or eskars the immediate neighbourhood 

 of Glasgow furnishes few and not very striking ex- 

 amples. A railway journey of less than an hour, 

 however, will take one to Ealkirk or Polmont, where 

 for several miles a characteristic kaim runs parallel 

 with the Edinburgh and Glasgow Railway. One 

 of the highest in Scotlaud, reaching 1,280 feet 

 above the sea, and therefore indicating a depres- 

 sion of the land to that extent at least during part 

 of the Glacial epoch, will be found crossing the 

 valley of Earl's Burn in the Campsie Hills, about 

 six miles south-west of Stirling. 



Of stratified tertiary deposits no vestige is known 

 to remain between the Grampians and the Southern 

 Uplands. But within easy reach of Glasgow are to be 

 seen many of those persistent dykes of basalt rock, 

 which, as Professor Geikie has shown, were con- 

 nected with the outbursts of volcanic activity, which 

 in Miocene times furnished the basaltic lavas of Mull, 

 Eigg, and the Giant's Causeway. In the region 

 with which we are concerned they run from east to 

 west. One of them has been traced with slight 

 intervals from the Firth of Clyde, near Helensburgh^ 

 to the Firth of Forth, near Grangemouth. Faults 

 cross it at every angle without deflecting its course, 

 and it pays no regard to the direction or degree of 

 dip of the stratified rocks. It crosses the Lower Old 

 Red sandstone, and all the subdivisions of the car- 

 boniferous formation represented in Scotland, in- 

 cluding the enormous thickness of porphyritic 

 lavas interbedded with the cement-stones below the 

 carboniferous limestone series. It may be followed 

 (with the Geological Survey Maps, Sheets 27, 28, 

 29, and 23, Stirling, in hand) across the Campsie 

 Fells, by starting at Ballewan farm-house, near 

 Blanefield station, Strathblane, and walking to 

 jjennv. a route affording in clear weather a mag- 

 nificent view over Glasgow, the mouth ot the Clyde, 

 Edinburgh, and the " black country" of Coatbridge 

 and Airdrie, as well as glimpses of the lovely 

 valleys of the Blane, and the "dark winding 

 Carron." The enormity of the strain that cleft 

 a passage for the molten rock, so direct, so long 

 (40 miles at least), so wide (sometimes 200 feet), 

 and through formations of every degree of tenacity, 

 may excite the admiration of even the mo^t blase 

 of geologists. Similar dykes may be traced from 

 Mugdock Castle, through the Loch Katnue 



