56 THE GEOLOGICAL HISTORY OP PLANTS. 



nucleus, and a wide translucent margin, marked by a 

 slight granulation. Even this, however, may indicate 

 nothing more than a different state of preservation. 



It is proper to observe here that the wall or enclosing 

 sac of these macrospores must have been of very dense 

 consistency, and now appears as a highly bituminous sub- 

 stance, in this agreeing with that of the spores of Lyco- 

 pods, and, like them, having been when recent of a highly 

 carbonaceous and hydrogenous quality, very combustible 

 and readily admitting of change into bituminous matter. 

 In the paper already referred to, on spore-cases in coals, 

 I have noticed that the relative composition of lyco- 

 podium and cellulose is as follows : 



Cellulose, Cj^Hj^Ogo. 



Lycopodium, C^gHig^NOg^. 



Thus, such spores are admirably suited for the pro- 

 duction of highly carbonaceous or bituminous coals, etc. 



Nothing is more remarkable in connection with these 

 bodies than their uniformity of structure and form over 

 so great areas and throughout so great thickness of rock, 

 and the absence of any other kind of spore-case. This 

 is more especially noteworthy in contrast with the coarse 

 coals and bituminous shales of the Carboniferous, which 

 usually contain a great variety of spores and sporangia, 

 indicating the presence of many species of acrogenous 

 plants, while the Erian shales, on the contrary, indicate the 

 almost exclusive predominance of one form. This con- 

 trast is well seen in the Bedford shales overlying these 

 beds, and I believe Lower Carboniferous.* Specimens of 

 these have been kindly communicated to me by Prof. 

 Orton, and have been prepared by Mr. Thomas. In these 

 we see the familiar Carboniferous spores with triradiate 

 markings called Triletes by Eeinsch, and which are simi- 

 lar to those of Lycopodiaceous plants. Still more abun- 



* According to Newberry, lower part of Waverly group. 



