DE LA BECHE ON GEOLOGICAL FACTS. 



71 



Such being the existing state of Geology, the unpretending volume 

 of M. De La Beche, can scarcely be too highly valued, inasmuch as 

 he rarely indulges in fancy and theory, and keeps rigidly to facts. Ac- 

 cordingly, when he does mention theories, and it would not be easy 

 to write on Geology without this, he usually introduces a caution ; for 

 example, "the student should be careful not to consider such expla- 

 nations as well-ascertained truths, but merely as hypotheses, which fu- 

 ture and extensive observations may or may not, prove to be correct." — 

 p. 177. Again " we have so few data for estimating the value of 

 this theory (LyelPs) that it can only be considered as a possible expla- 

 nation." — p. 7. In his preface also the author well remarks, that " it 

 is impossible to avoid hazarding certain general conclusions, when the 

 various known facts pass in review before us;" but "essentially it is 

 of little importance, whose or what theory may in the end be found most 

 accurate ; so long as we approximate towards the truth, we accomplish 

 all that can be expected ; and it is clear that the greater the amount of 

 known facts, the greater the chance of accuracy, not only from the 

 larger mass of information presented to the mind, but also from the 

 frequent checks offered to hasty conclusions." — p. vii. 



With so cautious and accurate a guide, then, as M. De La Beche, 

 the student need have no fear of being seduced from the path of truth 

 by brilliant but fallacious theories, so easy to frame but no less easy to 

 demolish by plain facts. It may be interesting to some of our readers 

 to have a specimen or two of our author's manner of treating his sub- 

 ject; and we may select almost at random, every part of the book being 

 carefully executed. We shall therefore take the first that offers, which 

 will prove that the author is an excellent field-observer as well as an 

 investigator of the labours of others. 



" Erratic Blocks and Gravel. 

 "From my own observations, I can fully confirm the remarks of vaiious authors 

 respecting the situation of the Alpine blocks, and their probable derivation from the 

 respective valleys which they, as it were, appear to face. But I have no where ob- 

 served such striking masses of erratic blocks as those which occur in the vicinity of the 

 lakes of Como and Lecco. They are particularly remarkable on the northern face of 

 the Monte San Primo, a lofty mountain ridge presenting one of its sides to the more 

 open and northern part of the lake of Como, where the latter stretches towards the high 

 Alps, thus presenting a bold front to any shock which should come from the north, 

 leaving open passages to the right and left of it, one down the southern part of the lake 

 of Como, the other down that of Lecco. Not only in front, facing the high Alps, but 

 also round the flanks and shoulders of this mountain, and even behind it, where the 

 eddy current would have transported them, blocks of granite, gneiss, mica slate, and 

 others from the central chain, of various sizes, and often accompanied by smaller frag- 

 ments and gravel, are seen in hundreds, nay thousands, scattered over the dolomite, 

 limestone, and slate of the mountain, and nearly filling up a previously existing valley 



