Geological Climate. 127 



their growth on the spot. Such evidence we seem to possess at two 

 distinct periods in the north of England, where we detect alterna- 

 tions of coal-beds, with their under clays, and limestones with marine 

 animal remains of the carboniferous time; and also find a coal accu- 

 mulation, with some plants, apparently in the position in which 

 they grew, of the oolitic series. In both cases the evidence would 

 be in favour of quiet depressions, low districts, with land plants grow- 

 ing upon them, so sinking beneath sea-water, that marine creatures 

 swarmed over the previous dry land, their remains entombed amid 

 detrital deposits effected at the time. 



Viewing the actual and varied altitudes above the sea-level of 

 lakes in different parts of the world, the plants which may be drifted 

 into them and preserved amid any mud, sand, or calcareous matter 

 deposited in such lakes, give us no just idea of the climate of the 

 time, at the sea-level in the same latitudes. For instance, the plants 

 drifted into the lakes of Switzerland and Northern Italy, some of 

 which may even be swept from heights approaching lines of perpe- 

 tual snow, would not give us the climate of the coast of the Bay of 

 Biscay between the Saone and the Gironde, though in the same general 

 latitude. Then, again, as to the conditions for the transport of 

 plants or their parts to situations where portions of them may be 

 more or less preserved in detrital matter, much has to be considered. 

 Though floods in high regions tear up trees and smaller plants in 

 their course, the chances of any of the plants reaching sea-coasts, 

 depend upon a variety of conditions, among which proximity to the 

 sea is one of no inconsiderable importance. Thus we have seen the 

 arborescent ferns and other plants of the higher lands of Jamaica 

 swept by floods into the adjoining seas (becoming entangled in part 

 among the mangrove swamps at the mouths of the rivers), the dis- 

 tance having been so short, that many stems of the fern tree, their 

 fronds, and those of other ferns of the higher regions, were not much 

 injured. No mere swelling of the rivers from rains on the lower 

 grounds, which did not cause torrents to wash away plants in 

 the higher lands, would bring down a frond of these ferns ; it would, 

 however, sweep on many a lowland plant, and not a few of those 

 which grew in the river courses during the dry weather, into the 

 mangrove swamps and the sea. 



In great rivers, the leaves, as they fall from trees overhanging 

 the water, are floated onwards and often cari-ied quietly to sea, some- 

 times fi-om long distances inland. Plants and their parts may, 

 under favourable conditions, be washed into, and be preserved in the 

 mud of climates where they do not grow. They may be thus 

 brought by the Mississippi, tlio Paraguay, the Nile, and the great 

 rivers of Northern Asia flowing from south to north, and be pre- 

 served imder climates differing from those where they flourished. 

 We have no reason to suppose that the conditions of continents, as 

 regards the flow of rivers into the sea, were not very various during 

 long lapses of geological time; and we should very carefully avoid 



