370 THE JOURNAL OF GEOLOGY. 



draw his conclusions as he could before the law of homotaxis 

 had been formulated." 



Thus, while admitting the possibility of homotaxial relations 

 existing between the floras of widely separated areas, certain cor- 

 relations, on the basis of simultaneity, of extensive series of beds 

 in different countries, have stood the test of time. On this sub- 

 ject Sir William Dawson has given important evidence.^ He 

 says: "I desire, however, under this head, to affirm my convic- 

 tion that, with reference to the Erian and Carboniferous floras 

 of North America and Europe, the doctrine of 'homotaxis,' as 

 distinct from actual contemporaneity, has no place. The suc- 

 cession of formations in the Palaeozoic period evidences a similar 

 series of physical phenomena on the grandest scale throughout 

 the northern hemisphere. The succession of marine animals 

 implies the continuity of the sea-bottoms on which they lived. 

 The headquarters of the Erian flora in North America and 

 Europe must have been in connected or adjoining areas in the 

 North Atlantic. The similarity of the Carboniferous flora on 

 the two sides of the Atlantic, and the great number of identical 

 species, proves a still closer connection in' that period. These 

 coincidences are too extensive and too frequently repeated to 

 be the result of any accident of similar sequence at different 

 times, and this more especially as they extend to the more mi- 

 nute differences in the features of each period, as, for instance, 

 the floras of the Lower and Upper Devonian, and Lower, Middle, 

 and Upper Carboniferous." 



USE OF FOSSIL PLANTS IN RESTRICTED AREAS. 



Turning now from the correlation of strata in widely separated 

 localities, we come to that part of the field in which geology is 

 likely to receive its most valuable aid from paleobotany, viz. : 

 the identification of horizons and their correlation within 

 restricted areas. While the phase of the subject which has just 

 been discussed may be of much importance when the final 

 volume of the geology of the world comes to be written, it can 



' Geological History of Plants, p. 262. 



