94 SKETCHES OF ORE ATI OK 



CHAPTER IX. 



DISCOVERY OF THE PROGRAMME. 



f | ^HE reader will have observed that the primal or Pots- 

 -**■ dam sandstone has been traced all around the circuit 

 of the central United States. There is no doubt that it 

 underlies all the region embraced within the circumference 

 of its outcrop. Indeed, at Columbus, Ohio, an artesian bor- 

 ing has probed the crust 2000 feet and more, and found this 

 sandstone in its proper place. At Lafayette, in Indiana, 

 Louisville, in Kentucky, St. Louis, in Missouri, and Chicago, 

 in Illinois, similar deep borings have been executed, and 

 the succession of strata, as far as the borings extend, has 

 been exactly such as geology expected ; and there can not 

 be a doubt, that wherever exploration should be made 

 throughout the wide extent of the area indicated, the 

 Potsdam sandstone would be found occupying its proper 

 position at the bottom of the Silurian series of strata. As 

 the same formation has been upheaved, at intervals, along 

 the whole distance to the Rocky Mountains, geologists 

 have arrived at the conclusion that the entire area of the 

 United States and Territories was, during the Lower Silu- 

 rian Age, the bed of a comparatively shallow sea. 



This conclusion leads to a generalization of the highest 

 interest. How came the central area of the North Amer- 

 ican continent a basin of shallow water? We can only 

 infer that, at this early period, the Alleghanies on the east, 

 and the Rocky Mountains on the west, had already begun 

 to be lifted above the general floor of the ocean. The Uni- 

 ted States were an immense continental lagoon — a subma- 



