EXTENT OF FOLDING AND SUBSEQUENT EROSION 459 



satisfies apparently all the characteristics of these deposits is that of a 

 huge subaerial delta fan, or a series of smaller confluent fans, formed 

 during a period of relative aridity and preceded by a period of more 

 pluvial conditions, during which white or gray quartz sands and pebbles 

 were spread out over part of the same territory occupied by the red beds, 

 but of less areal extent. The red beds along their margin dipped into 

 the sea and the deposits inclosed the remains of the marine organisms 

 then living. The greater part of the delta was, however, subaerial in 

 character, its head or heads being the old land of Appalachia, 100 or 

 more miles southeast of the easternmost outcrop of today. After the 

 deposition of an unknown thickness of such material, probably several 

 thousand feet in the southeastern area, deposition was interrupted by the 

 folding of the strata. This folding was the southward continuation of 

 the folding affecting the red Juniata and underlying beds to the north, 

 commonly known as -the Taconic folding. This occurred toward the end 

 of or after Eichmond time, as before noted. xYfter the folding erosion 

 was renewed, attacking this time the reel beds first and spreading the 

 material, resulting from this erosion, over the more or less eroded sur- 

 faces of the westward continuation of these same red beds. This consti- 

 tuted the southern equivalent of the Medina formation. The uncovering 

 of an underlying, unoxidized quartzite by erosion of the folded area fur- 

 nished the material for the later-formed pure Clinch sandstone. The 

 successive (1) red, (2) red, and (3) white beds of the northern and 

 southern Appalachians had thus a similar history and are of the same age 

 respectively. 



The Medina and the Tuscarora and Clinch formations and (heir exten- 

 sions in eastern United States. — The Medina beds of the Great Lakes 

 region. — The Siluric of eastern North America begins with the Medina 

 formation wherever that has not been removed by later erosion. In 

 Wisconsin and Iowa the base of the series is calcareous and rests on an 

 erosion surface of the Maquoketa (Eichmond) shales. In northeastern 

 Wisconsin a local deposit of iron ore separates the two formations, this 

 iron ore consisting of flattened pellets of uniform size and most probably 

 representing a replaced oolite. Irregular cross-bedding in the deposit, as 

 well as the arrangement of the individual grains, the absence of fossils, 

 and the local lenticular character of the deposit, all suggest an eolian 

 origin, the ancient calcareous ooids probably forming in a neighboring 

 saline lake or sea, being heaped up into dunes, to be subsequently covered 

 by marine deposits and later replaced by iron, probably in the form of 

 carbonate, which was then oxidized to the sesquioxide. As already noted. 



