84 GEOLOGICAL RECONNOISSANCE 



The chert slope at 340 feet in this section is nearly on a level with the 

 chert slope of the previous section. This formation seems to cap gene- 

 rally the subordinate ridges from 500 to 550 feet above Buffalo, but there 

 are other ridges, off to the south, which must be nearly double this height. 

 The rocks°which constitute the preceding sections, have the lithological 

 aspect and chemical composition of the rocks which form the hills on both 

 sides of the Upper Mississippi, between the mouth of the Chippewa and 

 Black river, and around Lake Pepin, referrible to the age of the Potsdam 

 sandstone and calciferous sand-rock of the New York system. 



Geology being decidedly a science of comparison and analogy, I may 

 venture to predict, in the absence of all systematic mining operations, 

 from my former experience in other similarly constructed countries of the 

 north-west, as well as from what has already been observed in Marion and 

 Carroll counties, in Arkansas, that lead ore will be found, to some extent, 

 in the rocks of Newton county ; but, in all probability, somewhat irregularly 

 disseminated in " pockets," " crevices," " strings," and horizontal openings 

 through the rocks, rather than in regular bodies ; hence, mining operations 

 will be attended with some uncertainty, and considerable labor and 

 expense; still, where the surface indications are encouraging, and the 

 calcareous rocks predominate over the sandstones, they maybe undertaken 

 by those having the necessary experience in rocks of this description, with 

 considerable prospect of success, so soon as the district is supplied with 

 furnaces for smelting the ore ; but not with as much profit to the miner as 

 in a cherty limestone, a member of the subcarboniferous formation, which 

 we shall have occasion to mention hereafter. 



In consequence of the southerly clip of the rocks, most of the strata of 

 the preceding sections disappear in succession beneath the waters of Cave 

 creek, as we ascend that stream. 



On the waters of Cave creek, about six miles above its mouth, a liver- 

 colored marble-limestone forms the base of a cliff, at an elevation of 10 to 

 20 feet above the bed of Cave creek, overlaid by cherty limestone. Several 

 nitre-caves have been formed by the disintegration of the liver-colored 

 marble limestone under the cherty limestone. The principal nitre-cave is 

 on the property of J. S. Thompson, on 'section 27, township 15 north, 

 range 19 west. 



The dark brown nitre-earth, which forms the floor of this cave, is rich 

 in salts of nitric acid, owing, no doubt, to the large quantity of organic 

 matter incorporated with the earth. The nitre-earth has been traced for 

 50 to 60 yards back into the cave, and for 7 to 8 feet in depth, mixed with 

 tumbled rock. 



Time has permitted, as yet, only a partial qualitative examination of 



