STRATIGRAPHIC SUMMARY. 627 



Lego. 



Waldron shale. 

 Laurel limestone. 

 Osgood beds. 

 Clinton limestone. 



The Laurel, Waldron and Lego together are represented by the 

 Glenkirk limestone in the Clifton section. 



In Kentucky and Indiana, the Louisville limestone succeeds the 

 Waldron shale, representing approximately the Lego and some 

 higher beds. In Arkansas, the St. Clair limestone represents early 

 Siluric (Niagaran). Its fauna allies it to the Alexandrian of 

 Missouri. In Oklahoma, the Siluric is represented by the Sylvan 

 shale resting disconformably on Richmondian and representing 

 Clinton or earlier horizons. Above the Sylvan shale, the Hunton 

 limestone in part represents Niagaran. The greater part of the 

 Hunton represents Helderbergian, a disconformity, representing 

 a great hiatus, dividing this limestone. In the Rio Grande region 

 of New Mexico and Texas, Siluric horizons have been recognized 

 in the Fusselman limestone (1,000 ft.).^^ 



On the Atlantic coast, the most important of the Siluric deposits 

 is the Anticosti group of Anticosti Island, and the local phases of 

 the same in Maine and eastern Canada. The fauna of this series 

 which represents Lower Siluric or Niagaran and possibly some 

 Middle Siluric, is distinct to a large degree from that of the Siluric 

 of the interior of North America, though many elements have been 

 found in common, especially with the " Clinton " of the southern 

 Ohio region. 



Other Siluric deposits are found in Alaska, where the Wales 

 series of southeastern Alaska and the Nome series of the Seward 

 Peninsula (including the Port Clarence limestone) are referred to 

 the Siluric. More doubtfully referred to this system are the Forty 

 mile series of crystalline limestones and schists of the middle and 

 lower Yukon regions, and the Skagit series of crystalline limestones 

 of northern Alaska. 



^ Richardson, G. B., " Palaeozoic Formations in Trans-Pecos Texas," A. J. S., 

 4th sec, Vol. XXV., 1908, p. 479. 



