[pENHALLow] NOTES ON TERTIARY PLANTS 63 



has been a remarkable recession of the genus since Cretaceous time, a 

 recession which has very nearly brought about its complete extinction. 

 Looking at more recent geological periods, however, we find that in the 

 [jignite Tertiary there were at least two species which ranged eastward 

 as far as latitude 104° W., and they therefore occupied at least a por- 

 tion of what is now the Prairie Eegion.^ One of these, S. langsdorfii, 

 is of very special interest in this connection because oi its very gener- 

 ally recognized relation to S. sempervirens, of which it constitutes the 

 ancesiral form, if it is not wholly identical with it, since it was practi- 

 cally co-extensive with Pseudotsuga in the Eocene age. Still later, how- 

 ever this same species is found in the Miocene deposits of Oregon, British 

 Columbia and the Valley of the Mackenzie river, in localities from 

 which the tree was long since withdrawn. Finally, it has been pointed 

 out by Sargent,- and more recently by Penhallow,^ that the genus 

 Sequoia must have been driven into its present narrow limits of dis- 

 tribution at a period not later than the glacial, and probably by the 

 very conditions which effected so marked an alteration of climate at 

 that time. AVe are therefore led to see that Sequoia and Pseudotsuga 

 were not only coextensive, but that their occurrence synchronized to so 

 late a period as the Tertiary, and possibly even to the glacial epoch; 

 and it is by no means an unwarranted assumption to conclude that the 

 ."^^ame causes which operated in the one case were also effective in the 

 other, and brought about a sudden diminution of the geographical area; 

 though, as is evident from the present range of the two species, these 

 causes did not operate with equal force in each case, but rather tendod 

 more strongly toward the obliteration of Sequoia. 



These conclusions then go far to show that the obliteration of the 

 Douglas fir from the Bozeman region may have taken place simul- 

 taneously with (the withdrawal from the Prairie region, which would 

 make the age of the Mystic lake deposits not later than Interglacial. 

 But such a conclusion can onJy be taken as a suggestion, since, as already 

 shown, glaciation in all probability continued at that locality to a later 

 period, and there is no evidence at hand to indicate that the genus was 

 not obliterated by wholly local causes, and that the deposits in which 

 it occurred were not similarly the result of local glaciation at a much 

 later period than the continental Interglacial. 



Th.e second specimen of wood already referred to as having been 

 transmitted to me by Dr. Knowlton was obtained by Mr. E. C. Eckel, 

 of Dalilonega, Georgia, by whom it was forw^arded to Dr. Knowlten. 



^ Tertiary Plants, Trans. R.S.C., IX.,iv., 41-43. 

 * Silva of North America. 



' McGill Univ. Mag., vol. 2, pp. 121 & 122. ; 



Sec. IV., 1904. 5. 



