250 ANNUAL OF SCIENTIFIC DISCOVERY. 



again poor, though retaining some of the Devonian species ; and it 

 goes on increasing up to the period of the Middle Coal-measures, and 

 this by the addition of species quite distinct from those of the Devonian 

 Period. 



3d. A large part of the difference between the Devonian and Car- 

 boniferous Floras is probably related to different geographical condi- 

 tions. The wide, swampy flats of the Coal Period do not seem to have 

 existed in the Devonian era. The land was probably less extensive 

 and more of an upland character. On the other hand, moreover, it is 

 to be observed that, when in the Middle Devonian we find beds simi- 

 lar to the underclays of the Coal-measures, they are filled, not with 

 Stigmaria, but with rhizomes of Psiloplnjton ; and it is only in the Up- 

 per Devonian that we find such stations occupied, as in the Coal-mea- 

 sures, by Sigillaria and Calamites. 



4th. Though the area to which this paper relates is probably equal 

 to any other in the world in the richness of its Devonian Flora, still it 

 is apparent that the conditions were less favorable to the preservation 

 of plants than those of the Coal Period. The facts that so large a pro- 

 portion of the plants occur in marine beds, and that so many stipes of 

 Ferns occur in deposits that have afforded no perfect fronds, show that 

 our knowledge of the Devonian Flora is relatively far less complete 

 than our knowledge of that of the Coal-formation. 



5th. The Devonian Flora was not of lower grade than that of the 

 Coal Period. On the contrary, in the little that we know of it, we 

 find more points of resemblance to the Floras of the Mesozoic Period, 

 and of modern tropical and austral islands, than in that of the true 

 Coal-formation. We may infer from this, in connection with the pre- 

 ceding general statement, that, in the progress of discovery, very large 

 and interesting additions will be made to our knowledge of this Flora, 

 and that we may possibly also learn something of a land Fauna con- 

 temporaneous with it. 



6th. The fades of the Devonian Flora in America is very similar to 

 that of the same period in Europe, yet the number of identical species 

 does not seem to be so great as in the coal-fields of the two continents. 

 This may be connected with the different geographical conditions in 

 these two periods ; but the facts are not yet sufficiently numerous to 

 prove this. 



7th. The above general conclusions are not materially different from 

 those arrived at by Goeppert, Unger, and Bronn, from a consideration 

 of the Devonian Flora of Europe. 



PKOGRESSIVE CHANGES IN THE CHARACTER OF THE PRAIRIES 



OF SOUTHERN ILLINOIS. 



Prof. Engelmann of the State Geological Survey of Illinois commu- 

 nicates to the American Journal of Science, some interesting observa- 

 tions on the progressive changes which are taking place in the charac- 

 ter of the prairie country of Southern Illinois. He says : In this dis- 

 trict, the prairie growth is undergoing a considerable spontaneous 

 change with the progressing settlement and cultivation of the country. 

 Since the prairie grass is no longer burnt off annually, as it used to be 

 by the Indians and early settlers, whereby all but the hardiest grasses 

 were destroyed, and those especially remained which propagate by 



