198 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



dish naturalist Celsius, demonstrated the untenable nature of such a 

 hypothesis ; it was he who first showed that these changes of relative 

 level are alone explicable by the movements of the land, and that a 

 permanent change of level of the sea, in detached regions of the 

 earth's surface, is physically impossible. " The imagination," he says, 

 " naturally feels less difficulty in conceiving that an unstable fluid 

 like the sea, which changes its level twice every day, has undergone 

 a permanent depression in its surface, than that the land, the terra 

 Jirma itself, has admitted of an equal elevation.. In all this, however, 

 we are guided much more by fancy than by reason ; for, in order 

 to depress or elevate the absolute level of the sea, by a given quan- 

 tity, in any one place, we must depress or elevate it by the same 

 quantity over the whole surface of the earth ; whereas no such ne- 

 cessity exists with respect to the elevation or depression of the land. 

 To make the sea subside thirty feet all around the coast of Great 

 Britain, it is necessary to displace a body of water thirty feet deep 

 over the whole surface of the ocean. It is evident that the simplest 

 hypothesis for explaining those changes of level, is, that they pro- 

 ceed from the motion, upwards or downwards, of the land itself, and 

 not from that of the sea. As no elevation or depression of the sea 

 can take place but over the whole, its level cannot be affected by 

 local causes, and is probably as little subject to variation as anything 

 to be met with on the surface of the globe*". 



Notwithstanding that this unanswerable doctrine was thus clearly 

 laid down so far back as 1802, we still find geologists of authority 

 speaking of the sea having risen or fallen, in their endeavours to ex- 

 plain certain phsenomena. I have within the last year heard this 

 said repeatedly in this room ; and in a recent excellent paper of my 

 friend Mr. Maclaren of Edinburgh, on Boulders and grooved and 

 striated Rocks observed by him on the shores of the Gare Loch iti 

 Dumbartonshire, an excellent observer, and in general a sound rea- 

 soner, I find such expressions as the following : — " The anomalous 

 presence of granite boulders at Gare Loch seems best explained by 

 assuming that they were floated on icebergs from Ben Cruachan, 

 Ben Nevis, or some other of the lofty granite mountains of the 

 north . . * . The sea must then have stood perhaps 1500 feet above its 

 present level, to permit the rafts of ice to pass over the lowest part 

 of the barrier. . . . An iceberg starting from the West or North 

 Highlands, and floating in a sea 1500 or 2000 feet above the present 

 level of the Atlantic, is an agent perfectly capable of effecting the 

 transportation of the stone, and offers, I think, the only conceivable 

 solution of the difficulty .... When the sea stood, as it certainly once 

 did stand, 1000 feet or more above its present level, a current would 

 set eastward through the gulf then occupying the low lands, of 

 which the estuaries of the Forth and Clyde form the extremities*" 

 Speaking of an ancient beach thirty-two feet above the present high 

 water line on the shore of Gare Loch, he says, " We may infer that 

 when the glacier occupied the valley of Gare Loch, the sea stood 

 ler than it does noiv by at least thirty feet, and probably a great 

 * Illustrations of the Huttonian Theory, p. 446. 



