EXTENT OF PALEOZOIC CONTINENTAL SEAS 305 



local differential oscillations of level. Much other evidence of a similar 

 nature will be found in succeeding parts. 



EARLY RICHMOND TRANSGRESSION 



For the first of these instances I have selected the Fernvale Richmond, 

 a shale and limestone formation rarelv exceeding 25 feet in thickness. 

 Often the shale is absent when the limestones come together into one or 

 more beds aggregating 2 to 5 or 6 feet in thickness. In its typical ex- 

 ]:)ression the Fernvale is limited to areas west of the Cincinnati axis. 



Whether followed directly by Niagaran, Devonian, or Mississippian 

 deposits, this thin limestone formation is present, except in very local 

 elevations, wherever the sea of the time can be shown to have extended. 

 Where it is absent the adjacent margin of the formation usually wedges 

 out by overlap, the proximity to a shore being further indicated by in- 

 crease in proportion of clayey matter. 



On the west flanks of the Nashville dome, also elsewhere, it has been 

 possible to establish approximate boundaries of baylike indentations to 

 which the Fernvale is confined. Being filled with highly characteristic 

 fossils, the bed is easily recognized. It has been studied at numerous 

 outcrops around the southern and western flanks of the Nashville dome. 

 In a northerly direction it has not been positively identified beyond Wil- 

 mington, Illinois, where it outcrops on the west limb of the Kankakee 

 axis. On the east and southern fianks of Ozarkia it is nearly always 

 found where beds of Mohawkian age were deposited, and in places it 

 overlapped these so that it rests on much older pre-Ordovician rocks. 

 Further, it is recognized in the Arbuckle uplift of Oklahoma as a 2 to 3 

 foot bed at the top of the Viola limestone by exactly the same lithologic 

 and faunal characters that mark it in southeastern Missouri. In many 

 places it is succeeded by a dark shale (the Sylvan) that can be shown to 

 be a southward extension of the Maquoketa of Iowa. 



In the bluffs of the Mississippi south of Saint Louis and north of 

 Riverside the bed can be followed for miles. Here it rests unconform- 

 ably on the peneplaned Kimmswick limestone, which is middle Mohawk- 

 ian in age. At one point (between Sulphur Springs and Spencer Sta- 

 tion) the Fernvale is succeeded by 16 to 25 feet of Maquoketa shale, and 

 this by a variable bed of sandstone regarded as the initial deposit of the 

 Kinderhook limestone. One-half mile south the Maquoketa has disap- 

 peared, bringing the Fernvale in contact with the Kinderhook. In the 



next two miles any one of several of the lower ledges of the Kinderhook 



yes. even the Keokuk — may rest on the Fernvale. The most significant 

 fact is that the Fernvale limestone is no thicker — it is usually about 



