TRANSACTIONS OP THE SECTIONS. 47 



duced disturbance. The igneous rocks were not that cause ; for they have them- 

 selves been disturbed, together witli the fossiliferous Lower Silurian rocks amid 

 which they lie ; and the mountainous character of the country, as it now presents 

 itself, is due, not to direct volcanic action, but to the unequal hardness of igneous 

 and aqueous masses, acted on by many denudations both ancient and modern, both 

 marine and subaerial. These causes, aided by faults wliich often brought hard and 

 soft rocks into immediate juxtaposition, have given rise to all the rugged outlines 

 on the surface of Wales, the hard rocks more strongly resisting decay and waste, 

 the soft ones yielding to time, the sea, and the weather, with gi-eater ease ; and 

 thus it happens that the hai-der masses generally form headlands, and the summits 

 of the moimtains, though often found elsewhere ; while the softer strata, wasted 

 away by the sea and by rain and rivers, are apt to lie in the recesses of bays and 

 in valleys and plains. This kind of argument I could equally well apply"^to the 

 Carboniferous formations of Scotland, where igneous rocks are rife, and, indeed, to 

 all those areas where igneous masses of ancient date are found intermixed with 

 sedimentary strata*. 



Again, if we go to the Alps, and look at the strata there, which are distiu-bed on 

 the greatest scale ; in all that part of the range that I best know, from east to 

 west for more than 100 miles in length, I have never seen a fragment of what I can 

 call a true igneous rock. Gneiss there is, and granite there is, which, according to 

 old ideas — a great advance in their day — some have been apt to classify either as 

 common igneous productions or as closely allied to them ; but no basalts or green- 

 stones, or rocks allied to these, play any important part in the structure of the 

 country, although the strata have been d'istm'bed in a manner of which no concep- 

 tion can be formed by those who have only studied such minor mountains as those 

 of the British Isles. There, in the Alps, we find areas as large as half an English 

 county, in which a whole series of formations has been turned upside down. But 

 by what means were masses of strata many thousands of feet thick bent and con- 

 torted and raised into the air so as to produce existing results by aiibrdiug matter 

 for the elements to work upon ? . Not by igneous or other pressure and upheaval 

 from below, for that would stretch instead of cnimpling the strata in the manner we 

 find them in great mountain-chains like the Alps, or "in less disturbed gi-oups like 

 those of the Highlands, Wales, and Cumberland, which are only fragments of 

 older mountain-ranges ; but, perhaps, as some have supposed, because of the radia- 

 tion from the earth of heat into space, producing gi-adually a marked shrinkage of 

 the earth's hardened crust, which, giving way, became crumpled along lines more 

 or less irregular, thus producing jjartial upheavals, though the bulk of the whole 

 globe was diminishing. A modihcation of this hypothesis does not attempt to 

 explain the positive cause of the shrinkage, but simply states, that from some un- 

 known cause, irrespective of radiation, great areas of the earth's crust having been 

 depressed, broad lines that lie between them have been contorted and heaved into 

 the ail- in the manner already indicated. Such shrinkage and crumpling, however 

 it was produced, when most intense and on the greatest scale, is always (where I 

 know it) accompanied by the appearance of gneissic or other metamoi-phic rocks, 

 and of granite or its allies ; and it has often been the custom to attribute the dis- 

 turbance of the strata in such mountain-ranges and their nietamorphism into 

 gneiss, crystalline marble, and the like, to the intrusion of granite. But my 

 opinion has long been that, -ft-ith regard to gneiss and granite, the first has been 

 produced by processes of nietamorphism which had no necessary connexion with 

 tlie intrusion of granite, while granite itself is often simply the result of extreme 

 nietamorphism, having passed through and beyond the stage of imperfect crystal- 

 lization, characteristic of gneiss, into that state of more perfect crystallization which 

 marks well-developed granite. If this be so, then, so far from the intrusion of 

 granite having produced such mountains as those I speak of, both gneiss and 

 granite woidd rather seem to be results of the forces that formed the mountain- 

 chains, I cannot tell how, but possibly connected with the heat produced by the 

 intense contortion of such vast masses of strata, the parts of which now exposed 

 by denudation were then deep undergroimd. There is, however, a difficulty here 



* This argument has of course no immediate application to existing or late Tertiary 

 volcanic areas, such as those of Auvergne, where entire and ruined craters still exist. 



