E. E. Hoicorth— Traces of a Great Pod-Glacial Flood. 553 



wliicli is an effect of decomposition. Apatite exists, and a few small 

 crystals of secondary epidote. There is some ilmenite covered with 

 leucoxene. If any bisilicate existed, it has decomposed. The effect 

 of decomposition is to give a quite different appearance imder the 

 microscope to that taken from the top of the liill. The hand 

 specimen looked, however, fairly fresh, and in appearance much 

 like the rock of Girn Dhu quarries. 



(I regret that we are unable to offer any chemical analyses of these 

 rocks, hut in our present locale we have no facilities for carrying 

 out such.) 



[To he continued^ 



VI. — Traces of a Great Post-Glacial Flood. 



5. Evidence of the Marine Drift. 



By Henry H. Hovokth, F.S.A. 



THERE is an unfortunate Nemesis attaching to great discoveries 

 and generalizations, which has not been sufficiently noticed. 

 When men have been floundering about for years in a quagmire of 

 confusion and difficulty, and some brilliant pen points out a clear 

 way by which the tangle may be threaded, — a way which is so 

 ingenious and simple that it at once seizes upon the current scientific 

 thought, and compels the adhesion of everybody, — it inevitably pro- 

 duces a period of stagnation and for a while dwarfs inquiry. What 

 is so palpably true and simple as the explanation of a very perplex- 

 ing difficulty is taken to explain all tlie difficulty, and, for a while at 

 all events, men's energies are devoted to bringing every apparently 

 aberrant and stubborn fact within the new law or the new process ; 

 and every effect, however remote, is traced hj a direct way or by a 

 zigzag to the prime cause which has proved so fruitful. It is only 

 after an interval, when men have digested and incorporated the new 

 theory into their daily creed, and it no longer ovei'awes them by its 

 freshness, that they are in a mood to ask soberly whether, after all, 

 too much has not been demanded from one cause, — -whether, after 

 all, the intricate and far-fetched explanations, which are necessary to 

 connect that cause .with effects with which we are familiar, is not 

 illegitimate, — and whether we must not supplement it by some other 

 cause, which has modified and altered its work, if we are to solve the 

 whole riddle. A very admirable concrete example of the matter we 

 are discussing may be found in the Glacial Theory. When the 

 Glacial Theory was proposed by Agassiz, working on the lines of 

 Playfair, to explain the rounded and polished surfaces we find in 

 Scandinavia and Scotland, the striated and farrowed rocks, and the 

 vast congeries of boulders of all sizes that strew the surface of 

 Northern Europe, it v/as felt that one of those critical turns had been 

 taken in Geology which enable iis to map out a vast and complicated 

 field with precision. Since this turn was taken it is surely no 

 exaggeration to say that the history of so-called Quaternaiy Geology 

 has been the history of the efforts made to explain every kind of 

 problem presenting itself in the surface deposits of Northern Europe 



