206 APPENDIX. 



to localities by the presence of carbonate of lime, magnesia, 

 oxide of iron, &c. 



" The uplands that border on the rapids are based upon 

 the mountain or carboniferous limestone, as the contained 

 fossils indicate. The limestone, of a dirty color, and mucli 

 broken up, is the matrix of numerous siliceous and calcareous 

 geodes. These fine geodes, picked up by all travellers, are 

 found on the banks of the rapids, having fallen from the 

 adjoining bluffs. Within a few years, there has been a road 

 opened leading to Warsaw, and, being cut off from the bluff, 

 has exposed to view the stratum in which the geodes occur, 

 and their position therein. They are observed to be slightly 

 compressed, their greater axes being parallel to the stratifica- 

 tion of the limestone, which is horizontal. As I have col- 

 lected a number of them, I shall describe, mineralogically, a 

 few of those that have appeared to me the most interesting in 

 their mineral association, viz.: — 



1 . Siliceous geodes, the cavity of which is filled with pris- 



matic crystals of limpid quartz (quarz hyalin). 



2. Siliceous geodes, filled with crystalline quarz, the pyra- 



midical terminations of which are of a red color. 



3. Siliceous geodes, filled with crystallized calcareous spar 



(variety, en tete de clou of Haiiy). 



4. Silico-calcareous geodes, with rhombic calcareous spar. 



5. Silico-calcareous geodes, with confusedly crystallized 



calcareous spar. 



6. Siliceous geodes, enclosing calcareous spar and crystalline 



sulphuret of zinc. 



7. Siliceous geodes, containing mamelonated chalcedony, of a 



red color. 

 " These geodes vary in size from four or five inches in 

 diameter to twelve or fifteen. 



" The following section exhibits the several subdivi- 



