xix. ANTIQUITY OF GRAVEL. 491 



mound of La Tiniere, left where the hrook quits its mountain 

 channel to fall into the Lake of Geneva, and mark the layers of 

 which it is formed, some below and some above the dispersed 

 reliquiae of Roman occupation, we can form a probable estimate 

 of the time employed in the accumulation of the whole, by the 

 admissible evidence of the time which has elapsed during the 

 accumulation of a part. Out of that mound, far below the Roman 

 line, there was taken in my presence, and under the eyes of my 

 companions, Mr. J. E. Lee and the late M. Morlot, a portion of 

 the cranium of a man, whose life-date might be stated to have 

 been some thousands of years before the palmy days of imperial 

 Rome. 



But here in our valleys no such marks occur ; our Saxon, Roman, 

 and British remains are never buried beneath layers of the gravel, 

 but always lie on its surface or in holes dug into it for burials, 

 wells, or dwelling-places. These gravels, then, are more ancient 

 than all known human occupation ; perhaps more ancient than even 

 that dimly understood period which we call pre-historic, marked 

 by the flint implements of early or even the earliest date, since 

 we have not in this part of the Thames drainage yet found these 

 implements deeply imbedded in the gravel by natural operations. 



Some long interval of time undoubtedly separates us from the 

 latest of the broad gravel-beds in the upper valleys of the Thames ; 

 the formation has practically ceased for thousands of years; the 

 physical conditions of the country have changed. What were the 

 conditions when the gravel was transported down the valleys of 

 the Thames ? 



Gravel is no longer accumulated, except in very small quantities, 

 because the water-forces exerted in the valleys are unequal to 

 transport it. The uplands are still wasted, and plenty of small 

 calcareous stones lie on the slopes, such as might make gravel-beds ; 

 but the rain and snow are less abundant, and the floods less 

 impetuous. The velocities of the existing currents, even in flood 

 time, would be quite incompetent to move the larger sort of 

 ordinary gravel, much less the large flints, larger corals, and greater 

 masses of rock which occasionally appear in the midst of these 

 irregular strata. To move some of these large masses would seem 

 to require the agency of shallow ice-rafts, formed in the valley 

 (not ice-bergs drifted from afar), because they lie not at the bottom, 



