602 METASPERMAE OF THE MINNESOTA VALLEY. 



Character of the Cretaceous flora. As has been shown in 

 the preceding chapter the main gorge of the Minnesota river 

 has, in part, existed since the times of the Upper Cretaceous, 

 and was possibly formed in even an earlier geological epoch. 

 The drainage might have been and probably was in the oppo- 

 site direction at that time, but from the presence of Cretace- 

 ous deposits in eroded portions of the Shakopee limestone we 

 know that at least the lower portion of the gorge was in exist- 

 ence before the formation of these deposits. At that time, as 

 shown by the remains of the Cretaceous flora of the Minnesota 

 valley which have been collected by Lesquereaux from the 

 Cottonwood valley localities, the basin supported species of 

 figs, sequoias, or "big trees," pines, laurels, magnolias, persim- 

 mons, poplars, willows and others. Of the twenty-eight spec- 

 ies described by Lesquereaux in his Cretaceous Plants of Minne- 

 sota, two are Conifers — one Sequoia and one Pinus — two are meta- 

 chlamydeous and twenty-four are archichlamydeous. This is 

 too small a collection to generalise from, but other collections 

 of Upper Cretaceous plants throughout the region of their oc- 

 currence in North America indicate the same general percent- 

 ages, so much in favor of supposing archichlamydeous plants 

 to have been in a greater preponderance among the total Meta- 

 spermaB than to-day. Regarding the physiognomic characters 

 of the flora it has been pointed out by Lesquereaux in 1874 

 that the indications are rather of a low-shore or morassic hab- 

 itat than of a distribution on drier hills. Under the law of 

 tensions we should expect to find the emergence of the newer 

 types upon just such territory, and the more favorable land 

 would doubtless have been occupied by the older types of 

 plants. This seems to the writer the true explanation of the 

 apparent suddenness with which metaspermic plants emerge 

 in the Cretaceous. The geologic formations in which they are 

 preserved are fit to preserve also the coniferous or cycadean 

 elements, if they were conspicuously present. That these are 

 less abundantly represented has generally been supposed to in- 

 dicate a preponderance of metaspermic elements in the gen- 

 eral flora. The facts seem, however, to indicate quite the re- 

 verse of this, and properly interpreted enable us to form a very 

 different picture of the Cretaceous plant-physiognomy. Under 

 the law of ejection of the weaker the sea- shore would pre- 

 sent a general tension-line and here would bo gathered in nar- 

 row strips, but extending somewhat up the rivers and distrib 

 uted in the marshes, the newer and struggling Metaspermao. 



