GEOLOGY. 225 



be connected with a limestone which was subsequently 

 observed in the Missisippi, between Prairie Du Chien and 

 St. Anthony, and in which we observed an oolite and a pul- 

 verulent limestone similar to the calcareous ashes described 

 by Mr. Freisleben in his elaborate account of the formations 

 of Thuringen. If we compare the characters of this rock 

 with those of the limestone observed by Mr. Freisleben, and 

 described by him under the name of zechstein and rauch- 

 wacke, we will be surprised at the great similarity in their 

 appearance. The zechstein is a compact, hard and tough 

 limestone of an ash-grey color, passing into blackish-grey, 

 distinctly stratified, without however presenting any slaty 

 appearance, or, at least, much less so than the inferior beds. 

 It contains specks and some veins of calcareous spar and 

 gypsum ; also crystals of quartz, &c. : it likewise offers 

 sometimes sjjecks of galena. It generally presents but few 

 petrifactions. Corallites and millepores, as well as several 

 species of terebratulites, ammonites, &c., have been found 

 in it. 



" Above this compact limestone another stratum of calca- 

 reous rock is found, which is known in the country under the 

 name of rauchwacke (smoky wack6). It is a limestone pro- 

 bably intermixed with silex, of a dark grey, sometimes 

 blackish color, with a somewhat scaly fracture, occasionally 

 fine-grained, sometimes, though seldom, oolitic, hard, tough, 

 and filled with pores or cavities : this last feature is charac- 

 teristic. It may be observed even in those parts of the 

 stratum which appear most compact. The cavities are 

 angular, long and narrow (as in a cracked clay). The inte- 

 rior of the cavities is lined with small crystals of calc-spar. 

 These cavities are sometimes large, being several yards in 

 length and breadth. He afterwards proceeds to describe the 



ashes or pulverulent substance found near it. This, from its 



11* 



