210 APPENDIX. 



contains in the proportion of ten per cent, at least. It con- 

 tains no potash, and but a small proportion of lime. It is a 

 very different mineral from that described by Dr. Thompson, 

 under the name of pipe-clay. 



" The predominant rock in this region of country to which 

 I am now referring — namely, from the Platte River to Coun- 

 cil Bluffs — is the carboniferous or mountain limestone, well 

 characterized by the fossils, consisting principally of the pro- 

 ducta lobata, producta punctata, orthis, delthyris, turbinolia 

 fungites, crinoidal remains, &c. ; most of these genera afford- 

 ing several new species as yet undescribed. 



'' This formation is a continuation of that which underhes 

 so vast an extent of the Missisippi Valley ; but having a 

 much larger development over the States that are to the east 

 of this river, and extending even to the Alleghanies. It is 

 the support of important coal-basins, and rests upon a group 

 of Silurian rocks, beginning at the Falls of St. Anthony, 

 extending itself from north to south, constituting the mine- 

 ral regions of Iowa, Wisconsin, and Missouri, and losing 

 itself somewhere in the State of Arkansas. This last-men- 

 tioned group is bounded at the north by amphibolic rocks, 

 steaschists, and clay slates, that extend to beyond 47° of N. 

 latitude ; and at the south also by steaschists and clay slates, 

 that compose the principal rocks at Little Rock in the State 

 of Arkansas, and also those of the Washita mountains. 

 These rocks are referrible to certain members of the group 

 to which Mr. D'Homaluis d'Halloy has given the name of 

 terrain ardoisier, and have their equivalent in the series of the 

 grauwacke of German geologists. Thus, by this distribu- 

 tion of the geological formations, it would seem that, more 

 particularly to the west of the Missisippi, the silurian group 

 is imbedded within the ' terrain ardoisier,' or grauwacke. 



