NATURAL HISTORY OF CREATION. 107 



a flood. Another associated phenomenon is that called 

 crag and tall, which exists in many places — namely, a 

 rocky mountain, or lesser elevation, presenting on one 

 side the naked rock in a more or less abrupt form, and 

 on the other a gentle slope ; the sites of Windsor, Kdiii- 

 l)urgh, and Stirling, with their respective castles, are 

 specimens of crag and tail. Finally, we may advert to 

 certain long ridges of clay and gravel which arrest the 

 attention of trav^ellers on the surface of Sweden and 

 Finland, and which are also found in the United States, 

 where, indeed, the whole of these phenomena have been 

 observed over a large surface, as well as in Eui-ope. It 

 is very remarkable that the direction from which the 

 diluvial blocks have generally come, the hnes of the 

 gi-ooved rock surfaces, the direction of the crag and tail 

 eminences, and that of the clay and gravel ridges — 

 phenomena, be it observed, extending over the northern 

 parts of both Europe and America — are all from the 

 north and north-ioest towards the south-east. We thus 

 acquire the idea of a powerful cui-rent moving in a 

 direction from north-west to south-east, carrying, besides 

 mud, masses of rock which furrowed the solid surfaces 

 as they passed along, abrading the north-west faces of 

 many hills, but leaving the slopes in the opposite direc- 

 tion uninjured, and in some instances forming long 

 ridges of detritus along the surface. These are curious 

 considerations, and it lias become a question of much 

 interest, by what means, and under what circumstances, 

 was such a current produced. One hypothetical answer 

 has some plausibility about it. From an investigation of 

 the nature of glaciers, and some observations which seem 

 to i]idicate that these have at one time extended to lower 

 levels, and existed in regions (the Scottisli Highlands an 

 (•i;aiijj)lc) where there is now no perennial >now. it has 



