191-'.] STEVENSON— THE FORMATION OF COAL BEDS. 543 



and covered a vast area with water, so as to spread the mingled 

 sediment of many water courses over the whole. 



The north-central portion of the Italian plain certainly resem- 

 bles closely a confluent flood-plain. The Adige emerges from its 

 valley just above Domigliana and, before reaching Verona, it is flow- 

 ing in the broad plain. It has brought down immense quantities of 

 very coarse material; for many miles it flows on a thick bed of 

 pebbles, derived in great measure from the Tyrolese Alps. At Ala. 

 where the river enters Italy, bowlders, 2 feet in diameter, are not 

 uncommon, but the surface material of the flood plain is not coarse, 

 except along the lines of filled watercourses. West from Verona, 

 along the railroad there is no rock exposure, all is river detritus. 

 At many places, the cobbles are so large that the peasants gather 

 them for construction of fences ; pebbles large and small are shown 

 in the railroad excavations between Verona and Milan, but they 

 are in sands ; the lines of stream flow are not shown in any exca- 

 vation visible from the road. The material decreases in coarseness 

 very quickly toward the south. Pavia is about 30 miles south from 

 Milan, but no coarse material is found there ; Piacenza is about 40 

 miles south from Brescia where the deposit is very coarse, but at 

 the former city the materials are fine. The Po has been crowded to 

 the south side of the plain, but it has changed its course many times 

 and the deserted channels are distinct. 



Morlot maintained that advance of the plain into the Adriatic 

 has been continuous in spite of long slow subsidence and he asserted 

 that, within the historic period, this subsidence has amounted to 

 5 feet; but the grounds for his assertion have been disputed. Evi- 

 dence exists which cannot be disputed, which proves long continued 

 subsidence. Challaye^** reported that a boring made by Dagousse 

 at Venice on the Piazza-de-Santa-Maria-Formosa passed through 

 132 meters of sand, clay and peat. Micaceous sand prevailed to 

 the depth of 25 meters and beds of peat were pierced at 29, 48, 85, 

 and 126 meters. He asserts that the peat in these beds is absolutely 

 the same as that forming now at several places within the lagoon. 

 Challaye finds evidence in this boring that, including the growth 



"" C. A. Challaye, Bull. Soc. GeoL de France, II., Vol. V., 1848, pp. 23, 24. 



