544 STEVENSON— THE FORMATION OF COAL BEDS. i^°^'- '. 



on the present surface, five forests have flourished on this spot. 

 Many borings have been made in this immediate area and the evi- 

 dence is consistent throughout. Tacconi^*^ has discussed the record 

 of one, which was driven 197 meters without passing beyond the 

 clays and sands. Well-marked peat beds were found at 18.80, 

 29.15, 32.80, 46.50, 56.70, 86.80, 129.80, 151.50 and thin streaks 

 down to 165 meters. It is quite possible that some of the very 

 thin streaks of carbonaceous material may be composed of vegetable 

 matter brought down during floods, but the suggestion of similar 

 origin for the thicker deposits, as made by some writers, cannot be 

 entertained. In view of what is known respecting the ability of 

 floods to remove the plant cover, the suggestion must be regarded as 

 pure assumption; the Po of the present day is confined within 

 dikes, yet it cannot sweep the enclosed narrow flood plain clear of 

 willows and underbrush ; there is no reason to suppose that the un- 

 confined stream was more efficient. Moreover, the material brought 

 up from the borings is peat, not a mere agglomeration of vegetable 

 material, but peat, such as now accumulates at the surface. 

 Tacconi emphasizes the fact that peat is more abundant in the upper 

 portion of the deposit, the important beds being within 18 and 59 

 meters; and he notes especially the bed at 18.80, which is 2.6 meters, 

 and that at 29.15, which is 6.25 meters thick, and. like some of the 

 others, contains wood. The lower beds are thinner and increasingly 

 impure, which leads him to suppose that conditions were less stable, 

 that the river courses were changed more frequently in the earlier 

 than in the later stages of deposit. The materials pierced by this 

 boring are mostly fine, only one layer of coarse stufT having been 

 found. The thickest clay bed is 8 meters and the thickest sand 

 deposit is 24 meters. 



The Mississippi region has been described so minutely by many 

 authors that only passing reference to some details is necessary 

 here. The delta, as usually limited, begins at a little way above the 

 Red River of Louisiana, but in Tertiary times the water area 



"" E. Tacconi, " Sulla composizione mineralogica della sabbia di un 

 pozzo trivellato al lido di Venezia," Atti R. 1st. Veneto, Vol. LXX., 191 1, 

 pp. 655-665. 



