290 THE WONDERS OF GEOLOGY. Lect. III. 



and the correlation between the organic and inorganic king- 

 doms of nature, during the tertiary epoch, were essentially 

 the same as at present. Dry land and water, continents 

 and islands, existed then, as now, — their geographical 

 distribution may have varied, — the temperature in certain 

 latitudes may have been much higher, — fertile countries may 

 have occupied areas now covered by water, and marshes and 

 fens have prevailed in regions now arid and waste ; but the 

 same agents of destruction and of renovation were then in as 

 constant activity as at present. It is true that immense num- 

 bers of large mammalia lie buried in regions where such crea- 

 tures could not now find subsistence, and in latitudes where 

 the climate is at this time unsuitable to such forms of 

 organization. But some of these apparent anomalies may 

 be explained by the fact, that the alluvial beds in which 

 these remains occur cannot have been the sites of the dry land 

 on which these extinct beings existed; they are the sediments 

 of ancient lakes — the deltas of former rivers — the estuaries 

 of seas — they are formed of the detritus of the land trans- 

 ported from a distance, and spread over areas then submerged 

 beneath the waters. If the Gulf-stream annually strews the 

 shores of the Hebrides with the fruits of torrid climes, the 

 currents of the ancient seas must have produced analogous 

 results ; and in our attempts to interpret past changes, it 

 must not be forgotten that they, have most probably been 

 produced by causes similar to those which are still in action. 

 I do not question the assumption, that some of the countries 

 containing these fossil remains, may have enjoyed a milder 

 climate during the tertiary ages than at present ; or that 

 in still more ancient periods there may not have prevailed 

 a much higher temperature ; but it appears to me, that the 

 variation of climate which a change in the relative distri- 

 bution of the land and water would occasion, as suggested 

 by Mr. Lyell,* — and a difference in the radiation of heat 

 * Principles of Geology, vol. i. chap. vii. 



