1865.] SIR R. I. MURCHISON ON GLACIERS. 27 



personal observations in the Alps, Carpathians, and Ural moun- 

 tains enable me to confirm this view. As regards the continent of 

 Europe, I should transport you to the Rhine, the Danube, and 

 other great streams, which, flowing through flat countries with 

 little declivity, never could have eroded those deep, abrupt gorges 

 through which they here and there flow, and which are manifestly 

 due to original ruptures of the rocks.* 



In holding these opinions as to the small power of watery or glacial 

 action, when not acting on an adequate incline, I do not doubt 

 that glaciers have been, and still are, most important agents in 

 modifying the outlines of mountains. Their summits are, we 

 know, continually degraded by rains and melted snows, and tor- 

 rents flowing down from them and carrying much detritus, are, 

 doubtless, deepening their channels wherever sufficient slopes 

 occur. But to whatever extent this agency has been and is at 

 work, and to however great a degree a descending glacier may 

 scratch and round off the rocky bottom on which it advances, I 

 coincide with Professor Studer, and with many other observers, that 

 the amount of erosion produced by these icy masses, particularly 

 when they have advanced into valleys where there is only a slight 

 inclination, must be exceedingly small. In valleys with a very 

 slight descent it will presently be shown that, even in the Alps, no 

 erosion whatever takes place, particularly as the bottom of the 

 glacier is usually separated from the subjacent rock or vegetable 

 soil by water arising from the melting of the ice. Again, in all 

 the steeper valleys down which ancient glaciers have formerly de- 

 scended, we do not find that either the sides or bottoms of the 

 upper gorges afford any proof of wide erosion, but only exhibit the 

 peculiar fashioning of the flanking surfaces of the rocks, or that 

 rounding off and polishing, called moutonni, accompanied with 

 striations. On the contrary, in gorges whence the largest glaciers 

 have advanced for ages, we meet with islands of solid rock and 

 little bosses still standing out, even in the midst of valleys down 

 which the icy stream has swept. 



With such proofs before us of what the frozen rivers called gla- 

 ciers have done and are doing in the high valleys, how can we 



* The recent Russian exploration of Eastern Siberia has shown how 

 the grand river Amur deflects suddenly at nearly right angles from its 

 course in a comparatively low country, to take advantage of a deep 

 natural rent in the mountains through which it escapes to the seaboard 

 (see p. 201 of the present Address to the Royal Geographical Society). 



