330 A. C. Ramsay on the Glacial origin of ‘certain Lakes 
sloping valley or gorge, but (excepting little swallow-holes) it 
cannot form and deepen a profound hollow, so as to leave a 
rocky barrier all round: though it may fill with sediment one 
that had previously been formed. 
Thirdly, neither do most of the Swiss lakes lie in lines of dis- 
location. For many reasons, I do not believe that any one of 
them among the high Alps or on their flanks can be proved to 
lie in lines of mere gaping fracture. Let us consider the nature 
of such fractures. 
generally a simple displacement of the strata up or down, on 
one side or the other; or, if the disturbance go beyond this, 
it is that along the sloping line of fracture the beds on the 
downthrow side are turned up, and those on the opposite side 
bent down, by pressure and slipping combined. In more dis 
turbed districts, like the Welsh Coal-measures, the same phe 
nomena are observable: witness, for instance, the numerous 
sections from accurate observation, drawn on a true scale, by 
Sir Henry Dela Beche, Sir William Logan, and others. Ex- 
perience, both above ground and in mines, proves the same. 
Most lodes are in fractures, and many lie in lines of fault. In 
metamorphic, excessively contorted, and greatly fractured dis- 
tricts, like those of Devon, Cornwall, and the cracks, 
whether bearing metals or not, vary from mere threads to 4 few 
fathoms in width. They are always filled with quartz or ob 
foreign substances, frequently harder than the surrounding ae 
trix. I have often traced lodes on the surface, in Wales, by sa 
hard matter filling the crack standing in relief above the suria® 
of the softer enclosing rock. In limestone rocks the ener oe 
usually partly filled with crystallized carbonate of lime. ail 
fracture are not, therefore, for purposes of denudation, “des 
sarily lines of weakness, unless it happen that on opposite § 
of the fault hard and soft rocks come together, wally 
e softer rocks will wear away more rapidly, and gene 
originate a straight valley. 
+ ea in an catia contorted country, such as ee an 
i ’ 
it is, I believe, impossible, in consequence of that contort yee 3 
there should be gaping fractures now exposed to view. +: 
ing for the koi der the sudden violent contortio? 
the strata of any great tract of country, we shall see th4 pe 
contorted rocks now exposed at the surface, even if broken, W° 
be most unlikely ¢ 
mec to gape. : ee 
_ The expression “elevation of mountains” conveys to the minds 
when of course 
hat the 
