426 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



They are suggested by the restriction of the middle Devonian Grand 

 Tower limestone to the southeastern and southern sides of Ozarkia. No 

 deposits corresponding in age to the greater, lower part of this limestone 

 are known to the north of St. Louis where, on the contrary, we find 

 formations of late Devonian ages that are not represented by sediments 

 on the southern flanks of Ozarkia. Indeed, excepting the lower part 

 of the "New Albany shale,'^ which is probably of Devonian age, no 

 unquestionable late Devonian deposits are known in Kentucky, Ten- 

 nessee, Arkansas, and Oklahoma. In the next succeeding earliest Missis- 

 sippian stage Ozarkia was tilted to the southeast on which side we find 

 black shale, and often the basal sandstone, of the Chattanooga formation. 

 The deposits of this age are not evenly distributed on the flanks of -this 

 uplift, but are found locally on the south and east sides in what I 

 believe to have been larger or smaller embayments of the old shoreline. 

 Before the close of the stage a considerable arm of the sea extended up 

 the Mississippi Valley beyond the northern extremity of the Ozarkian 

 uplift into southern Iowa, where the Sweetland shale is thought to rep- 

 resent this age, and to Chicago, where remains of fishes suggesting 

 the same age are found in subterranean solution channels in Silurian 

 dolomite. 



Succeeding the Chattanooga the attitude of the area was reversed, 

 the Louisiana limestone and equivalent deposits being found only on 

 the northern and western flanks. That it was soon again tipped to 

 the southeast is shown by the Glen Park limestone, which contains an 

 interesting derivative of the southern Atlantic Hamilton fauna and has 

 been found only on the east side of the uplift. Next comes the more 

 or less arenaceous or calcareous Hannibal shale which is rather generally 

 found on the north and west flanks but has not been recognized on the 

 east side south of St. Louis nor on the south border in northern 

 Arkansas. The upper limestone of the Chouteau has much the same 

 distribution about Ozarkia as the Hannibal, but the following Fern 

 Glen zone, though far from occurring in a continuous outcrop, probably 

 encircled the island. The distribution of the Fern Glen fauna suggests 

 general subsidence, but as the formation does not outcrop on the north- 

 west side there must have been some tilting toward the southeast. The 

 Burlington overlaps the Fern Glen to the north in Iowa as well as all 

 around the Ozark island except on the east side. In fact, as is shown 

 by remnants preserved in sink holes scattered over a large part of the 

 dome, the Burlington probably transgressed from the west, north and 

 south to the crystalline nucleus of Ozarkia. 



