i82 NATURAL SCIENCE. March, 1894. 



the localities of fossil plants their position shall be fixed by strati- 

 graphical evidence. This being done in a few cases, it is not difficult 

 to assign to their approximate position intermediate or allied sub- 

 floras. In Canada, though the collections of fossil plants have not 

 been so large as would be desirable, we are fortunate in having the 

 horizons of the leading floras accurately fixed by the officers of the 

 Geological Survey, and the plants collected carefully referred to the 

 beds to which they belong. 



Thus, though the geographical conditions of the Mesozoic and 

 Cainozoic are not of such a character as to enable us to refer 

 sub-floras to their definite geological position throughout the whole 

 Northern Hemisphere in the manner in which this can be done for 

 the plants of the Lower, Middle, and Upper Carboniferous, neverthe- 

 less, a satisfactory approximation can be made, and I have no 

 hesitation in affirming that it is possible to define with considerable 

 accuracy the age of any collection of fossil plants from any part of 

 our Cretaceous or Cainozoic districts. 



Plants as evidence of geological age have the advantage of wide 

 distribution over the surface of the land, and of long duration in any 

 one place, and slowness of migration when obliged or enabled to 

 spread to new localities. They are also so closely connected with 

 the great movements of subsidence and elevation which mark the 

 lapse of geological time, that they are very certain indices of these,, 

 whether they affect plant life directly by elevation and submergence, 

 or indirectly by changing the climatal conditions. 



As in the case of animal fossils, we have to allow for differences 

 of station, for possible driftage and intermixture of species belonging 

 to uplands and low levels, and varieties dependent on chances of 

 deposition and preservation. We have also to consider that plants 

 are more permanent and less changeable than the animal inhabitants 

 of the land, so that they may not mark such small portions of time or 

 such minute changes as may be indicated, for example, by mammalian 

 remains. 



On the whole there is very good reason to believe that the 

 labours of Palaeobotanists have, in the United States and Canada, 

 succeeded in securing for fossil-plants an important place as guides in 

 the determination of geological age. The knowledge we have 

 acquired needs to be collected and arranged in such a manner as to 

 make it more available than it can be when scattered, as at present, 

 through a great number of reports and memoirs. 



J. W. Dawson. 



