312 Horner's Geological Address. 



alone explicable by the movements of the land, and that a per- 

 manent 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 firma 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 quantity, in 

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

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

 necessity 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 tha*t the simplest hypothesis for explaining those 

 changes of level, is, that they proceed from the motion, up- 

 wards 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 any- 

 thing 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 explain certain phenomena. 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 Edin- 

 burgh, on boulders and grooved and striated rocks observed 

 by him on the shores of the Gare Loch in Dumbartonshire, an 

 excellent observer, and in general a sound reasoner, I find 

 such expressions as the following : — " The anomalous pre- 

 sence of granite boulders at Gare Loch seems best explained, 

 by assuming that they were floated on icebergs from Ben Cru- 

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

 of the north . . . The sea must then have stood perhaps 1500 



* Illustrations of the Iluttonian Theory, p. 446. 



