82 ERA OF THE SUPERFICIAL FORMATIONS. 



apparently the produce of some vast flood, or of the sea 

 thrown into an unusual agitation. It seems to indicate that, 

 at the time when it was laid down, much of the present dry 

 land was under the ocean a supposition which we shall see 

 supported by other evidence. The included masses of rock 

 have been carefully inspected in many places, and traced to 

 particular parent beds at considerable distances. Connected 

 with these phenomena are certain rock surfaces on the slopes 

 of hills and elsewhere, which exhibit groovings and scratchings, 

 such as we might suppose would be produced by a quantity 

 of loose blocks hurried along over them by a flood. Another 

 associated phenomenon is that called crag and tail, 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, Edinburgh, and Stirling, with their respective 

 castles, are specimens of crag and tail. Finally, I may 

 advert to certain long ridges of clay and gravel which arrest 

 the attention of travellers 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 Europe. It is 

 very remarkable that the direction from which the diluvial 

 blocks have generally come, the lines of the grooved rock 

 surfaces, the direction of the crag and tail eminences, and 

 that of the clay and gravel ridges phenomena, be it ob- 

 served, extending over the northern parts of both Europe and 

 America are all from the north and north-west towards the 

 south-east. We thus acquire the idea of a powerful current 

 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 direction unin- 

 jured, and in some instances forming long ridges of detritus 

 along the surface. These are curious considerations ; and it 

 has become a question of much interest, by what means, and 

 under what circumstances, such a current was produced. 

 But in the present state of our knowledge, all that can be 



