GEOLOGICAL SKETCH 295 



waves of sand. The summits could be seen creeping 

 insidiously onward, pouring down the smothering sand 

 and engulfing every obstacle in their relentless path. 

 They were a real miniature of the sand-dunes of the 

 desert ever rolling onward and burying beneath their 

 debris the cities of men. I calculated the rate of 

 movement of one of these folds and estimated that 

 in every twenty-four hours it advanced down stream 

 one-sixteenth of a mile ; and though one glance at the 

 moving sand shows that the change varies in rapidity 

 in different parts of the stream, yet it is perhaps a fair 

 estimate to say that in sixteen days every mile of 

 the bed of this gentle stream has been rolled another 

 mile nearer to the sea. 



And as grain rolls upon grain and layer rolls upon 

 layer to build up a fold of sand, so also does fold roll 

 upon fold. Smaller folds roll up the gentle slopes 

 of greater folds and greater folds roll down on smaller 

 folds. As the curling crests of ocean billows pour 

 down their foam to overwhelm the smaller waves 

 before them, so do the larger waves of sand pour 

 down their foam of granules on the wavelets that 

 precede them. 



Thus grain upon grain, layer upon layer, fold upon 

 fold is rolling, but the revolution will not end here. 

 At length on the bed of the ocean the sand-grains 

 come to rest. Vast deposits, thousands of feet in 

 thickness, are built up beneath the sea. After a 

 long lapse of time the strata are consolidated, up- 

 heaved, exposed to the erosion of new rivers which 

 again roll down their sand. The last stratum to 

 be deposited will be the first to be denuded, and 

 the fragments of each older stratum will be laid down 



