Bocks altered by Glaciers and by Water compared. 107 



moving mass, is especially distinct in limestone rocks, where 

 grooves are seldom nicely cut, but present the appearance of 

 a violent pressure combined w^ith the grooving power, thus 

 giving to the groove a character which is quite peculiar, and 

 which at once strikes an observer who has been familiar with 

 its characteristic aspect. Now, I do not know upon what 

 the assertions of some geologists rest, that gravel, moved by 

 water under strong heavy currents, will produce similar 

 effects. Wherever I have gone since studying these pheno- 

 mena, I have looked for such cases, and have never yet found 

 modern gravel currents produce any thing more than a 

 smooth surface, with undulating furrows following the cracks 

 in the rocks, or following their softer parts ; but continuous 

 straight lines, especially such crushed lines and straight fur- 

 rows, I have never seen. 



When we know how extensive the action of water carry- 

 ing mud and gravel is on every shore and in every water- 

 current, — when we can trace this action almost everywhere, 

 and nowhere find it similar to the phenomena just described, 

 I cannot imagine upon what ground these phenomena are 

 still attributed to the agency of currents. This is the 

 less rational as we have at present, in all high mountain 

 chains of the temperate zone, other agents, the glaciers, 

 producing these very same phenomena, with precisely the 

 same characters, to which therefore a sound philosophy 

 should ascribe, at least conditionally, the northern and alpine 

 polished surfaces, and scratched and grooved rocks, or at 

 least acknowledge that the effect produced by the action of 

 glaciers more nearly resembles these erratic phenomena than 

 does that which results from the action of currents. But 

 such is the prejudice of many geologists, that those keen 

 faculties of distinction and generalization, that power of 

 superior perception and discrimination, which have led them 

 to make such brilliant discoveries in geology in general, seem 

 to abandon them at once as soon as they look at the erratics. 

 The objection made by a venerable geologist, that the cold 

 required to form and preserve such glaciers, for any length 

 of time, would freeze him to death, is as childish as the appre- 



