FOSSIL PLANTS. 477 



stant recurrence of the same species at the same place, and a diversity only at 

 a distance in various directions. 



At Mazon creek, the meanders of the stream have dug a broad bed through 

 the same bank of shale, and the water, washing for centuries, has uncovered 

 great numbers of concretions and scattered them for miles from their point of 

 origin. As a whole, therefore, the concretions represent the characters of the 

 flora of a large area. No other place in the Illinois coal field has afforded the 

 same advantages for research. 



The shales al Colchester, Murphysborough and St. Johns, are rich in vege- 

 table remains; but little has been done there in the way of collecting speci- 

 mens of fossil plants, except by the assistants in the Survey. And from the 

 above remarks it is easy to understand that researches made in passing, or re- 

 maining at a place only for a short time, are far from affording the chances of 

 valuable discoveries. It is, therefore, very probable, that these last named locali- 

 ties have still in reservation a good many species of coal plants which are now 

 unknown to us, and that the fossil flora of Illinois is far from being fully 

 known at the present time. 



The Report on the Flora of the Coal Measures of Illinois should have been 

 closed here, but for the recent publication of a remarkable work on vegetable 

 palaeontology. (1) Among other matters of general interest, this work is pre- 

 faced by some discussions on the cause and nature of phenomena attending the 

 preservation or fossilization of vegetable remains. It also describes and critically 

 reviews most of our new species published in the 2d vol. of the Ills. Geol. Re- 

 port. This, of course, is a reason for considering, from American observations, 

 some well established facts which corroborate or invalidate the conclusions of 

 the celebrated author. It also provokes a discussion on the value of some of 

 our species, and on their affinity with the flora of the Carboniferous Measures 

 of Europe. And further, it now becomes of importance to review the conclu- 

 sions which have already, or should be hereafter drawn, on the geographical 

 and stratigraphical distribution of our species of fossil plants in relation to geol- 

 ogy, and to fix some reliable points of reference for future researches on the 

 subject. 



(1) Traite de Paleontologie vegetale par W. Ph. Schimper. Paris, Bailliere & fils, 1869. 



