81 



ERA OF THE SUPERFICIAL FORMATIONS 



EXISTING SPECIFIC FORMS ABUNDANT. 



WE have now completed our survey of the series of stratified 

 rocks, and traced in their fossils the progress of organic crea- 

 tion down to a time which seems not long antecedent to the 

 appearance of man. There are, nevertheless, memorials of still 

 another era or space of time which it is all but certain did 

 also precede that event. 



The first that calls for notice is the phenomenon to which 

 geologists have applied the term denudation. Great hitches 

 and slips are detected in superficial strata, such as, if left in 

 their original state, must have caused considerable inequalities 

 on the face of the country ; yet all is found as smooth the 

 joinings are all as much reduced to a common level as if 

 some gigantic artificial force had been used for the purpose. 

 Again, a great valley has been scooped out in the midst of 

 sedimentary strata, leaving the edges of these facing each 

 other from the opposite sides, with perhaps here and there an 

 isolated mass starting up to the height of the two sides, being 

 composed of matter which has resisted the agency by which 

 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 

 formations of all eras, in various parts of the globe, but con- 

 fined in general to situations not very elevated, there is a 

 layer of stiff clay, mostly of a blue colour, mingled with 

 fragments of rock of all sizes, travel-worn, and otherwise, 

 and to which geologists give the name of Diluvium, as being 



