96 ERA OF THE SUPERFICIAL FORMATIONS. 



the adjoining matter was removed. Here, it is thought, we 

 see incontestable traces of the operation of moving water. The 

 second fact we are called to notice is, that over the rock forma- 

 tions of all eras, in various parts of the globe, but confined, in 

 general, to situations not very elevated, there is a layer of stiff 

 clay, often of a blue colour, mingled with fragments of rock of 

 all sizes, travel-worn, and otherwise, and to which geologists 

 give, or till lately gave, the name of Diluvium, as being ap- 

 parently 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, possibly one in 

 which there were large rafts of ice. Another associated 

 phenomenon is that called crag and tail, which exists in many 

 places, namely, a rocky mountain, or lesser elevation, pre- 

 senting on one side the naked rock in a more or less abrupt 

 form, and on the other a gentle slope. Finally, we may ad- 

 vert 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 North America, 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 gene- 

 rally 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, it is to be observed, extending over the 

 northern parts of both Europe and America are mostly from 

 the north and north-west towards the south and- south-east. We 

 thus acquire the idea of a powerful current, a commixture of 

 water and ice, 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 uninjured, and in some instances forming long ridges 

 of detritus along the surface. These are curious considerations j 

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



