1912] STEVENSON— THE FORMATION OF COAL BEDS. 483 



ing at times, calcareous nodules. The deposit is without pebbles and 

 becomes increasingly sandy toward the west. The Pampean forma- 

 tion resembles the Pittsburgh reds. Gruner"- has observed that in 

 the Loire basin, red beds are not uncommon in the sterile stage of 

 Saint-Chamond. The deposits are found at all horizons in this for- 

 mation which is from 650 to 2,600 feet thick and is tlie middle divi- 

 sion of the Loire Coal Measures. In the Lancashire field of England 

 the reds appear to be confined to the upper Coal Measures. 



Dawson found abundance of ripple marks, rain and footprints in 

 the Acadian red shales but no record of such markings on the Penn- 

 sylvanian reds has come to the writer's notice. Fossil remains, 

 vegetable or animal, are rare, but Raymond*'^ discovered reptilian 

 bones in a small basin eroded in the sandstone on which the Pitts- 

 burgh red shales rest. Not infrequently the red muds contain nodules 

 of ferruginous limestone in which are marine fossils ; these abound 

 in the Pittsburgh reds and cause much annoyance to drillers of oil 

 wells. At one locality in West \^irginia on the east side, the Pitts- 

 .burgh reds are replaced with a succession of variegated shales which 

 are exceedingly rich in marine forms, several of which pass upward 

 into the Ames limestone ; and the shales are similar at 25 miles 

 southwest. The Pittsburgh reds, at least in part, were deposited 

 where salt water had access. There is much to suggest similar 

 origin for some other reds. Those below the Cambridge pass upward 

 to that limestone as the Pittsburgh reds pass to the Ames. In con- 

 siderable areas they replace the limestones and the two deposits are 

 continuous with each other or even with the Washington reds above. 

 The limestones are wedges in the shale as the ^laxville becomes a 

 wedge in the Mauch Chunk shales within southern Pennsylvania. 

 The Washington reds are equivalent in position to the Birmingham 

 shales at Pittsburgh, which Raymond, in the publication cited above, 

 has shown to be marine. It is certain that marine conditions are in no 

 wise antagonistic to deposition of red shale. At tiie same time, one 

 must not forget that the conditions must have been very difiFerent 



*^L. Gruner, " Bassin houiller de la Loire," Paris. 1882. p. 217. 



** P. E. Raymond, " A Preliminarj^ List of the Fauna of the Allegheny 

 and Conemaugh Series in Western Pennsylvania," Topog. and Geol. Surv. 

 (of Penn), 191 1. p. 89. 



