CONCLUSIONS TO BE DRAWN FROM FOSSILS. 



79 



and that these grew on vast marshy or partially submerged tracts of 

 level alluvial land. We have, moreover, distinct evidence of old 

 land-surfaces, both in the Coal-measures and in other cases (as, 

 for instance, 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. 17). 



Conclusions as to Climate. 

 — In many cases fossils enable us 

 to come to important conclusions 

 as to the climate of the period in 

 which they lived, but only a few 

 instances of this can be here ad- 

 duced. As fossils in the majority 

 of instances are the remains of 

 marine animals, it is mostly the 

 temperature of the sea which can 

 alone be determined in this way ; 

 and it is important to remember 

 that, owing to the existence of 

 heated currents, the marine cli- 

 mate of a given area does not ne- 

 cessarily imply a correspondingly 



warm climate in the neighbouring land. Land-climates can only be 

 determined by the remains of land-animals or land-plants, and these 

 are comparatively rare as fossils. It is also important to remember 

 that all conclusions on this head are really based upon the present 

 distribution of animal and vegetable life on the globe, and are 

 therefore liable to be vitiated by the following considerations : — 



a. Most fossils are extinct, and it is not certain that the habits and 

 requirements of any extinct animal were exactly similar to, or even 

 at all resembling, those of its nearest living relative. 



b. When we get very far back in time, we meet with groups of 

 organisms so unlike anything we know at the present day as to 

 render all conjectures as to climate founded upon their supposed 

 habits more or less uncertain and unsafe. 



c. In the case of marine animals, we are as yet very far from 

 knowing the exact limits of distribution of many species within our 

 present seas ; so that conclusions drawn from living forms as to 

 extinct species are apt to prove incorrect. For instance, it has 



Fig. 17. — Erect Tree containing Reptilian 

 remains. Coal-measures, Nova Scotia. (After 

 Dawson.) 



