136 SKETCHES OF CREATION. 



and the south of Georgian Bay. The Corniferous is north 

 of Lake Erie and beneath Lake Huron. The Mountain 

 limestone is farther toward the centre of the continent, in 

 the Mississippi Valley. The Laramie limestone stretches 

 to the Rocky Mountains. If the reader can fix his imag 

 ination on each of these great limestone belts, he has a clew 

 to a mental map of the geology of the country. 



In the little map on the preceding page I have endeav 

 ored to indicate the locations of the great limestone masses 

 just alluded to (except the Laramie limestone, w r hich is too 

 far west). The horizontal shading shows the trend of the 

 Lower Silurian mass, which, in Ohio and farther west, is 

 not discriminated from the Cincinnati Group. Its pro 

 longation into Wisconsin is covered up with surface sands 

 and clays. The vertical shading indicates the trend of the 

 Upper Silurian mass, which is also lost in Wisconsin. In 

 Ohio it probably exists in a belt encircling the Lower Si 

 lurian area, but it has not yet been completely traced out. 

 The oblique shading from right to left denotes the great 

 Devonian mass (corniferous limestone), which has not yet 

 been distinctly traced beyond Lake Michigan. The ob- 

 lique shading from left to right is the Mountain lime 

 stone, or Lower Carboniferous mass, which I have pro 

 posed to designate the Mississippi Group, because so ex 

 tensively developed in the valley of the Mississippi River. 

 Now, if the reader desires to know to what particular for 

 mation any proposed limestone quarry belongs, this little 

 map will inform him. The letter C indicates the areas 

 which are underlaid by the coal-measures of the country. 

 In the Northern States these are the uppermost strata of 

 solid rock. Hence all other formations dip toward the 

 nearest coal-measures, and generally pass under them. In 

 other w r ords, all the strata numbered from 1 to 3 dip to 

 ward the areas marked C. It follows, also, that Nos. 2 and 



