204 TERTIARY TIMES. 



resemblance in all the phenomena, physical and vital, than 

 it was possible to trace between the present and any of the 

 remoter epochs.* 



As Eocks there is nothing difficult to comprehend either 

 in the nature or composition of the tertiary sediments. In 

 one basin or area of deposit we have alternations of sands, 

 gravels, clays, and lignites ; in another, sands, gravels, clays, 

 limestones, gypsums, and lignites; and in a third, clays, 

 lignites, marls, and interstratified overflows of lava or showers 

 of volcanic ashes. All these alternations are well displayed 

 in the tertiary basins of London, Hampshire, Paris, Au- 

 vergne, the Lower Ehine, and Vienna; and the observer 

 has no greater difficulty in comprehending the nature of 

 these successions than he has in interpreting the sediments 

 of any lake or estuary of the present day. In. some basins 

 the limestones may be hard and compact, or even siliceous, 

 like the burr-stone of Paris ; in others the sands may be 

 consolidated into sandstones ; in some, the lignites may be 

 peaty and woody, while in others they are scarcely distin- 

 guishable from ordinary coal ; but taking them all in all, 

 the tertiary strata present few difficulties either as regards 

 composition or the agencies concerned in their formation. 

 In some of the areas of deposit, as evidenced by their fossils, 

 the strata are strictly marine, in others they are fresh-water 

 or lacustrine, and in some, again, there is an admixture of 

 sea and river silts, which are consequently regarded as estu- 

 arine or fluvio-marine. Just as at the present day such 

 seas as the Adriatic, Euxine, and Caspian are receiving their 



* The reader who will take the trouble to consult a geological map of 

 Europe will see at a glance that much of the continent was occupied by 

 seas and lakes during the Tertiary period, and that it was not till towards 

 the close of the epoch that as a land-mass it began to assume its existing 

 configuration and dimensions. As with Europe, so to a great extent 

 with Asia and Africa, but notably so with North and South America. 

 The great land-masses had then been merely blocked out, as it were ; their 

 existing aspects are the results of Tertiary and Quaternary modifications. 



