FOSSIL FLORA OF THE STAFFORDSHIRE COAL FIELDS. 333 



wherever we find a sudden extinction of the organic life in any stratum, we are not to 

 suppose that such extinction was universal. In most cases it must have been com- 

 paratively local, for a total extinction would imply a new creation of the same forms in 

 every succeeding stage of strata in which they are met. The most probable supposition 

 is, that during all the long geological ages in which our fossiliferous strata were being 

 deposited, or from the first appearance of life on our globe, there never has been, at any 

 one time, a total extinction of the flora or fauna from the remote period till the present 

 time ; and when we find in our Coal Measures the constant reappearance of certain well- 

 known species after each local extinction, in higher and higher stages of strata in the 

 same locality, we are naturally led to conclude that, while they become extinct over 

 these tracts, they must have continued flourishing in other parts of our Carboniferous 

 sea, and that they spread from these spots into their old localities wherever the condition 

 of the sea-bottom again became favourable to their growth and development." In a 

 letter, dated October 26, 1887, he further says: — "There can be no doubt of the 

 repeated occurrence in higher and higher horizons of many of the marine and fresh 

 water forms of life found in our Scottish Coal Measures. Since this paper (that quoted 

 above) was printed, I have been able to trace other forms besides Lingula, that range 

 from the very lowest fossiliferous marine beds up into that of the Permian Formation. 

 It is, therefore, quite unsafe to take any one organism as characteristic of any special 

 horizon, for closer investigation of the strata in any country is constantly proving their 

 recurrence or occurrence in higher or lower beds." 



Now, with organisms possessed with the property of locomotion, this is quite what 

 may be expected. As the conditions became unfavourable for their growth and existence, 

 they would remove to more suitable situations. Of course, conditions may arise which 

 are unfavourable to the life of organisms that previously flourished in a given locality ; 

 and should no favourable conditions arise or exist within suitable distances for migration, 

 there would be a total local extinction of species, which, perhaps, might extend over 

 large areas, but that such occurrences were not universal is evidenced by the repeated 

 recurrence of species in higher and higher zones, separated by great masses of strata 

 destitute of their remains. 



In regard to plants the case is different. They being fixed to the localities in which 

 they grow, are of necessity obliged to succumb should any subsidence or unfavourable 

 condition for their growth arise, and did the conditions again become favourable, de- 

 scendants from the original individuals could never more return. 



Of course, similar species were no doubt flourishing in other localities, and when the 

 subsided area had again been elevated into dry land, it might have been peopled with 

 new individuals of the same species, and it is true that certain species again revisit the 

 old haunts of their kindred, but it is only comparatively few that ever do so, and with 

 them they always bring new 7 associates. Thus the change in the flora gradually pro- 

 gresses. 



It is also true that there are vast masses of rock that show little change in their flora, 



VOL. XXXV. PART 6. 3 I 



