PROFESSOR HUXLEY OX THE WAR-PATH. 57 



impresses this ignorance upon us even as regards some of the 

 simplest of her operations. Sometimes it is difficult to under- 

 stand the conditions of original deposit. Very often it is still 

 more difficult to understand the conditions of denudation or re- 

 moval. The great earth-movements which have certainly taken 

 place are full of mystery the depressions and elevations, the 

 cracks and " faults " which have dislocated the strata, the " down- 

 throws/' sometimes of thousands of feet, which have cut across 

 the rocks as sharply as if the cutting had been eif ected by a knife, 

 the overthrows and the overthrusts, the sinkings and the under- 

 thrusts, which have inverted the order of original formation, the 

 metamorphism which has obliterated original structure here, and 

 has left it wholly unaltered there ; the vast thicknesses which 

 are destitute of the remains of life, in juxtaposition perhaps with 

 some one thin bed which is crowded with them ; the methods by 

 which, and the times during which, old forms of life have been 

 destroyed, and new forms have been introduced all these, and 

 a thousand others, are questions on which our ignorance is pro- 

 found. 



Now, it is a remarkable fact that all these difficulties are, as it 

 were, multiplied and accentuated in that very period which is 

 nearest to us that period which was marked by the very latest 

 changes of which geology has any cognizance I refer to the period 

 which is now generally called Quaternary. It is sharply marked 

 off from previous periods by a strictly scientific definition. Shells, 

 and particularly marine shells, may be called the time-medals of 

 creation. Their comparative indestructibility, and the fact that 

 the element in which their inmates live is the same element which 

 preserves their habitations when they die, make it certain that in 

 them Geology keeps her oldest, most complete, and most authentic 

 record. The Quaternary period is defined as that during which 

 innovation was stopped as regards the development of shell-life 

 during which no new species was born during which we find, 

 with a few rare exceptions, no shell which is not also an existing 

 and a living species. As regards them, therefore, the Quaternary 

 period is the existing period in the classifications of geology. It 

 is the age in which we ourselves are now living. And yet this is 

 the very period during which the greatest novelty of all seems to 

 have been introduced, for it is in this period that we can first de- 

 tect the advent of man. Moreover, it is in this period that there 

 seem to have been some of the most mysterious earth-movements 

 of which the science has any glimpse. Great dislocations of strata 

 great changes in the distribution of land and sea great destruc- 

 tion of preceding forms of life, are among the familiar conceptions 

 which its best-ascertained phenomena suggest. Nor is this all. 

 The vanishing of preceding forms of life in many older periods 



