CONCLUSIONS TO BE DRAWN FROM FOSSILS. 55 



their present position to the fact that their former owners were 

 drowned in rivers or lakes, or carried out to sea by streams. 

 Birds, Flying Reptiles, and Flying Mammals might also simi- 

 larly find their way into aqueous deposits; but it is to be re- 

 membered that many birds and mammals habitually spend a 

 great part of their time in the water, and that these might there- 

 fore be naturally expected to present themselves as fossils in 

 Sedimentary Rocks. Plants, again, even when undoubtedly 

 such as must have grown on land, do not prove that the bed 

 in which they occur was formed on land. Many of the remains 

 of plants known to us are extraneous to the bed in which they 

 are now found, having reached their present site by falling into 

 lakes or rivers, or being carried out to sea by floods or gales of 

 wind. There are, however, many cases in which plants have 

 undoubtedly grown on the very spot where we now find them. 

 Thus it is now generally admitted that the great coal-fields 

 of the Carboniferous age are the result of the growth in situ 

 of the plants which compose coal, and that these grew on vast 

 marshy or partially submerged 

 tracts of level alluvial land. 

 We have, however, distinct 

 evidence of old land-surfaces, 

 both in the Coal-measures and 

 in other cases (as, for in- 

 stance, in the well-known 

 " dirt-bed " of the Purbeck 

 series). When, for example, 

 we find the erect stumps of 

 trees standing at right angles 

 to the surrounding strata, we 

 know that the surface through 

 which these send their roots 

 was at one time the surface of 

 the dry land, or in other 

 words, was an ancient soil 

 (fig. 19). 



In many cases fossils en- 

 able us to come to important 

 conclusions as to the climate 

 of the period in which they 

 lived, but only a few in- Fig. 19.-Erect Tree containing Reptilian 

 stances of this can be here remains. Coal-measures, Nova Scotia. 



, ., (After Dawson.) 



adduced. As fossils in the 



