74 ANTIQUITY OF LIEGE CAVE-BONES. CHAP. iv. 



fluctuations are afforded by gravel containing elephant's 

 bones at slight elevations above the Meuse and several of its 

 tributaries. The loess also, in the suburbs and neighbor- 

 hood of Liege, occurring at vai*ious heights in patches lying 

 at between 20 and 200 feet above the river, cannot be 

 explained without supposing the filling up and re-excavation 

 of the valleys at a period posterior to the washing in of the 

 animal remains into most of the old caverns. It may be 

 objected that, according to the present rate of change, no 

 lapse of ages would suffice to bring about such revolutions 

 in physical geography as wo are here contemplating. This 

 may be true. It is more than probable that the rate of 

 change was once far more active than it is now. Some of 

 the nearest volcanoes, namely, those of the Lower Eifel 

 about sixty miles to the eastward, seem to have been in 

 eruption in post-pliocene times, and may perhaps have been 

 connected and coeval with repeated risings or sinkings of the 

 land in the basin of the Meuse. It might be said, with 

 equal truth, that, according to the present course of events, 

 no series of ages would suffice to reproduce such an assem- 

 blage of cones and craters as those of the Eifel (near An- 

 dernach, for example); and yet some of them may be of 

 sufficiently modei-n date to belong to the era when man was 

 contemporary with the mammoth and rhinoceros in the basin 

 of the Meuse. 



But, although we may be unable to estimate the minimum 

 of time required for the changes in physical geography above 

 alluded to, we cannot fail to perceive that the duration of 

 the period must have been very protracted, and that other ages 

 of comparative inaction may have followed, separating the 

 post-pliocene from the historical periods, and constituting an 

 interval no less indefinite in its duration. 



