284 IDENTITY OF THE WESTERN FORMATIONS 



depression produced by a synclinal axis, and from thence the 

 strata gradually rise to the westward. 



The limestone soon rises from beneath the river-level, and 

 continues in view nearly to the Mississippi, being obscured only 

 by superficial accumulations. After ascending the Mississippi 

 for some distance, the rock again appears. The great valley, or 

 " American bottom," is bounded on either side by abrupt chffs of 

 this limestone ; the river meandering in its course from side to 

 side, sometimes runs at the base of the perpendicular rock, whUe 

 the opposite side presents a broad level bottom land, covered for 

 the most part with luxuriant forests of primeval growth. These 

 cliffs form some of the most picturesque scenery, and, with the 

 small shot towers upon the overhanging margin above, suggest 

 the idea of stupendous castle walls of Cyclopean architecture, 

 crowned with the sentinels' towers. 



Between the point of its first appearance on the Mississippi 

 and its final disappearance near the mouth of Rock river, I ex- 

 amined it at numerous points, and always found a very uniform 

 lithological character, which alone is sufficient to distinguish it 

 from all other rocks, and enable one to identify it with its com- 

 mencement in Indiana. The fossils, however, are constant and 

 unemng guides, which left no room for doubt. The rock, on 

 fresh fracture, has a peculiar light gray color, much of it crystal- 

 line, while other portions are compact and fme-grained, present- 

 ing the appearances described at Leavenworth. 



At St. Louis I obtained several fossils, principally corals and 

 crinoidea, all of which, so far as I know, differ from those found 

 in any lower rock. Dr. B. B. Brown, of St. Louis, politely pre- 

 sented me with specimens of Productus, from his cabinet, which 

 were found in that vicinity, and which correspond with the 

 British P. Martini. Having since had an opportunity of exam- 

 ining a small collection of fossils from the carboniferous lime- 

 stone of England, in the Lowell Institute, I found many of the 

 same species as those of this great formation, leaving no doubt 

 of the identity of the two. The difficulties, therefore, in the way 

 of comparing our rocks with those of Europe, seem in a fair way 

 to be cleared up, and we learn that among all our limestone 

 formations, in the eastern part of the United States, the true car- 



