120 ORIGIN OF BRITISH ISLES. 



the Firth of Lome, are trough-like folds of the kind named syn- 

 clinal. This is manifest at once from the fact that the regions of 

 the firths are composed of basins of newer Primary rocks, while the 

 intervening mountainous regions consist of the older Primary rocks 

 from which the newer deposits have been worn away, if they were 

 ever deposited upon them. 



Scotland probably originated in the elevation of the Grampians, 

 which were at first, as Professor Judd l has demonstrated, a chain of 

 active volcanoes which poured out enormous quantities of angular 

 fragments and sheets of lava during much of the Old Red Sandstone 

 and Carboniferous periods. But it is unlikely that the folds which are 

 now to be seen determining the direction in which the rocks of Scot- 

 land extend, were fully developed until the close of the Primary 

 period, and all these folds appear to be a consequence of a great com- 

 pressing force acting from the north-west towards the south-east. It 

 would be a mistake, however, to speak of them as having formed 

 Scotland at this early period, unless we remembered that Scotland 

 was merely a portion a south-western prolongation of the Scandi- 

 navian land. JSTor can we consider this folding of the rocks without 

 bearing in mind that it is parallel to other ancient folds forming 

 mountain chains near the eastern coast of North America, and that 

 the bed of the Atlantic itself is thrown into mountain ridges, one of 

 which extending from Rockall on the north-west of Scotland runs 

 south-westward far beyond the Azores to the mouth of the Orinoco. 

 Everything in geological history leads us to believe that the great 

 folds of the earth's crust having once been made, undergo no impor- 

 tant change in direction in the successive geological ages. They 

 may be modified chains which were high may sink beneath the 

 ocean ; they may be broken up by folds which cross them transversely, 

 but the evidence of their existence endures in the contorted rocks, 

 and we are thus aided in determining the relative antiquity of our 

 shores. It is probable that the old land thus indicated was connected 

 on the south with the region which is now Normandy and Brittany. 

 The Cambrian rocks of Wicklow correspond with those of North 

 Wales; the Carboniferous and Old Red Sandstone strata of South 

 Wales, which run nearly east and west, are continuous with the cor- 

 responding rocks in the south of Ireland. There these deposits occupy 

 folds which are alternate saddles and troughs similar to those which 

 are prolonged farther south by the rocks of Somerset, Devon, and 

 Cornwall, continuous with the folds of Belgium, and parallel to 

 those of the North of France. But here the direction of the resistance 

 to the compressing force has changed, and hence the strike of the strata 

 is almost due east and west in the south, although the intermediate 

 angles can be traced in Wales and the adjacent English counties suffi- 

 ciently well to demonstrate that there is no conclusive reason for 

 assigning a much later date to the southern than to the northern com- 

 pressions. If the latter took place during the great elevation of land 

 at the close of the Permian period, the former are not more recent 

 1 Quart. Jour. Geol. Soc., vol. xxx. p. 289. 



