TERTIARY SANDS. 



97 



superficial stratum of extensive sand plains, and by the application 

 of fertilizing substances, it has made them abundantly productive 

 of vegetable life." 



From the information supplied, it appears that many inland expanses 

 of sand drifts may be considered a resuscitation of sand deposits, 

 which may have been quiescent for ages, fixed naturally by a similar 

 mantle of vegetation to that by which man is artificially arresting 

 and utilizing the same sand drifts or others situated elsewhere. 

 With sand drifts on the sea coast it is to a great extent otherwise, 

 though in some, even of these, there may be seen a resuscitation of 

 sand previously partially fixed by vegetation in some of the earlier 

 stages of the operation whereby extensive regions of sand dunes have 

 for ages been confined. 



Several of these are spoken of as belonging to the Tertiary forma 

 tion, in explanation of which term it may be stated : 



Geologists, in classifying the stratified layers of mineral substances 

 covering the granite, consider that those of gneiss, and schist, and 

 clay slates, were first deposited, and these are described by them as 

 primary formations. Following these in order, and in many cases 

 superimposed on them, are sandy slates, silurian limestones, and 

 what is known as the old red sandstone. These are described by 

 them as transition formations. They are followed by mountain lime- 

 stone, coal beds, magnesian limestone, new red sandstone, shell lime- 

 stone, lias limestone, oolite limestone, chalk beds, and green sand ; 

 and these are designated secondary formations. Above these are 

 found blue and plastic clays, marls, and limestones, sands, and 

 calcareous grits ; and these are spoken of as tertiary formations ; and 

 above this, indicative of a later deposit, are diluvial clay deposited 

 from seas or lakes, and boulders, alluvial clay deposited by rivers, 

 and sand and gravel ; and overlying these, the vegetable soil resulting 

 from the decomposition of vegetable mould, and the admixture of the 

 products with the superficial mineral layer. 



From this it appears that the sand now spoken of is supposed to 

 have been deposited in times long past. 



An account has been given, cited from Boitel, of thejway in 

 which, on the Landes of La Sologne, heaths on these old sands are 

 planted with the maritime pine. In other inland situations we find 

 these sands of the tertiary formation throughout extensive districts 

 covered with forests of trees of other kinds, varying according to 

 conditions and circumstances — such, for example, is the famous forest 



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