252 RECENT FORMATIONS. 



lower and middle of these terraces in Britain, Trance, and 

 other European countries, that the bones of the mammoth 

 and woolly rhinoceros have "been exhumed, along with the 

 flint implements of rude and primitive races ; and were the 

 river-deposits of the other continents geologically examined, 

 there is no doubt they would exhibit in a similar way a gra- 

 dation from the events of the current century back to those 

 bordering on the tertiary epoch. As it is, these river-deposits 

 play an important part in the physical geography of every 

 country, their rich and well- watered surfaces presenting the 

 finest fields, whether for forest-growth, pasture, or cultivation. 

 We have only to name the principal rivers of the world to 

 recall to the geographical reader the alluvial expanses that 

 mark the most of their courses, and these in magnitude 

 according to the volumes of the respective rivers and the 

 flatness of the country through which they flow. And 

 even where magnitude is not concerned, these river-deposits 

 are not without their importance. Every gully from the 

 mountain-side has its. terminal spit of sand and gravel, 

 and it is often in such deposits, worn from the cliffs and 

 veins above, that we find the most abundant and readiest 

 supplies of the gems and precious metals as witness the 

 diamond-conglomerates of Brazil and India, the tin-gravels 

 of Cornwall, and the gold-sands and shingle of California, 

 Columbia, Australia, New Zealand, and the Oural. These 

 auriferous sands and gravels are but the debris of the older 

 mountain-cliffs disintegrated by the frosts and rains, and 

 carried down by the streams to the lower " creeks " and 

 "gullies," where, accumulating for ages, they are often of 

 great thickness, and carry us, in many instances, far back 

 even into the tertiary period. Many of the Australian 

 gold-gravels, indeed, are surmounted by thick overflows of 

 basaltic lava, and as volcanic agency has long ago ceased to 

 manifest itself in these regions, these show at once the vast 



