36 GEOLOGY OF LA SALLE COUNTY. 



mg plants, but they are nol coal. Then we find what 

 we are sure can be nothing- but the trunks of larg-e 

 trees, but they are hard, blue limestone, yet there are 

 the roots, the trunk, the branches as perfect as 

 they w^ere myriads of ag-es ag-o. We find them in 

 abundance both in connection with the coal and in the 

 slates and shales, always stone or pyrite, never coal. 

 The question then arises, is coal ^ veg-etable product? 

 Certain it is that the sigfillaria, the lepidodendron, the 

 calamite, cordaites and the ferns did not contribute to 

 the formation of coal, and if plants did, under an}^ cir- 

 cumstances, become coal, they were mosses similar in 

 some respects to sphag'num and hypnum, and were 

 first transformed into peat. Prof. James D. Dana, 

 lately of Yale University, than whom a hig-her au- 

 thority and a more conservative student cannot be 

 quoted, tells us in his Manual of Geolog-y, p. 712-14, 

 that not less than eight cubic feet of veg-etable matter 

 would be required to make a cubic foot of coal, and he 

 would be inclined to say more than that, probabl3^ten 

 cubic feet for one of coal! At the least of these 

 figures a ten-foot bed of coal requires a layer of vege- 

 tation not less than eig-hty feet thick, and the- 

 mammoth bed at Potisville a layer not less than 

 576 feet thick! Whence could such a mass of vegeta- 

 ble matter come? 



We said above that the vegetation of the carbon- 

 iferous period in our region was not dense. Every- 

 thing goes to prove this, and we are decidedly of 

 the opinion that such a vegetation as today encumbers 

 the delta of the Ganges and that of the Niger, 

 the valleys of the Irrawady and Amazon, and the 

 western declivities of the Cascade range in Oregon 

 w^as unknown to this age. The theory is that 

 there w^as more carbonic acid g-as in the atmos- 



