668 c. schuchert devonian of oklahoma 



Middle Devonian 



In the region of Marble City the thin Oriskanian is followed by the 

 Sylamore sandstone, of which Dunbar saw a thickness of about 5 feet. 

 TafT, on the other hand, in his Tahlequah Folio speaks of the Sylamore 

 as being variable in thickness, and says that in the vicinity of Marble City 

 it is between 20 and 30 feet thick, followed by about 20 feet of Chatta- 

 nooga shale. While in the field, Dunbar measured 50 feet of black shale ; 

 so that between them there is no discrepancy as to thickness. We may 

 therefore say that there is of the Sylamore sandstone at least 5 feet, but 

 that there may be between 20 and 30 feet. Taff notes further, however, 

 in places farther north, that the next higher formation, the "Chattanooga 

 black shale," rests directly on the Saint Clair marble of Middle Silurian 

 age. It is plain, therefore, that the whole of the Sylamore may be locally 

 absent, and that this absence is not due to a lack of deposition as a sand- 

 stone lentil of the Chattanooga, but to erosion. This is made clear by the 

 following statement from TafT. The Sylamore sandstone, he says, "termi- 

 nates abruptly at the top in Walkingstick Hollow [only a few miles to 

 the northwest of Marble], where the contact is clearly exposed. At one 

 locality noted in this valley, where the erosion of the stream had just 

 reached the top of the sand, the surface is uneven, the black shales filling 

 irregular depressions a foot and less in depth and 2 to 3 feet in width. 

 The contact between the shale and the sand is clean, no sand being in- 

 cluded in the shale, even in the basin-like depressions" (page 3). 



Dunbar was so fortunate as to find some characteristic brachiopods in 

 loose blocks from the basal 5 feet of the Sylamore sandstone, and they are 

 all forms of the Camden, a formation once regarded as of Oriskanian age, 

 but now known to be of earliest Middle Devonian time. 5 These species 

 are listed in the section described on a later page. 



TafT, in the Tahlequah Folio, says the only fossils collected by him in 

 the Sylamore sandstone are "more or less macerated fragments of large 

 fish bones, apparently of the genus Dinichtliys," and more rarely small 

 fish teeth. As the bones of the "terrible fish" are more often found in 

 the Upper Devonian, he concluded that the Sylamore was a sandstone 

 lentil, followed without break by the "Chattanooga black shale," and that 

 both are of late Devonian time. However, as fish bones are common in 

 the Onondaga and as Dinichtliys also occurs here, it is seen that this evi- 

 dence for age determination is not so reliable as the brachiopods, all of 

 which are of Camden species or of earliest Ulsterian time. 



5 Dunbar : Op. cit. pp. 88-90. 



