IOWA ACADEMY OF SCIENCES. 53 



doubtful whether there is another locality where such peculiar forms of calcite are 

 found, two varieties beingr associated toarether in the stalactites. The latter have 

 also undergone a change in structure since first formed. The caves were discov- 

 ered by Mr. Baule, of Dubuque, while prospecting for lead. They are openings in 

 the crevices of the Galena limestone like those in which the lead and zinc ores 

 occur. Large and productive crevices have been worked less than a half mile to 

 the north, and the spar-bearing fissures also carry lead at a lower horizon. Fol- 

 lowed west out on to the high prairie land back from the river these crevices are 

 marked by sink holes, and on a winter day the moisture is seen rising from them. 

 The magnesian limestone of the region is cut by innumerable large and small 

 fissures that at certam horizons form extensive openings that can be followed for 

 thousands of feet, and form a labyrinth of underground passages. All the latter 

 are formed by approximately east and west, north and south, and "quartering" 

 crevices. The openings vary in size from those so small that one can scarcely 

 force his way through, to others having a width of ten or twelve feet and height of 

 five feet. Some are over forty feet in height. 



These caverns are either empty or filled entirely or in part by clay. The 

 deposits of lime carbonate occur only in certain portions of these openings where 

 the moisture is most abundant. At these points the top and bottom are decorated 

 with stalactites, stalagmites, and a wonderful variety of beautiful and fantastic 

 forms. The passages are in places closed up by thick deposits requiring blasting to 

 remove them. Strong currents of air pass through these caves and are doubtless 

 instrumental in producing the curious formations. 



In these underground passages two varieties of calcite occur. 



1. Satin spar, formed of radiating fibers with silky luster. Color'ess and 

 white varieties both occur, 



2. Argentine (Schieferspath). This variety has a pearly luster and is com- 

 posed of more or less undulating lamellse. Color, white. It agrees with the descrip- 

 tions given by Dana and Tschermake for Argentine, and is to all appearances that 

 variety of calcite. The latter author mentions it as occurring in Bohemia, Saxony 

 and Cornwall. 



Satm spar occurs in several different forms: (1) Includes those which are 

 pearly white, on the surface of fracture and have a silky luster due to the radiating 

 fibers that form a velvety surface of great beauty. This variety occurs in bunches 

 or clusters of twisted and gnarled stem-like forms. (2) Includes those stalactites 

 proper which are formed of radiating fibers. These have in cross section a sub- 

 vitreous luster, but on the surface they are (a) either covered with a fine white 

 powder (which under the microscope is seen to be composed of irregular grains or 

 minute crystalline bodies), and have no luster, or (b) the outer surface is formed of 

 little rhombohedrons and has a silky luster. These stalactites are white or color- 

 less, opaque or translucent. 



There are still other stalactites differing from any of the above that have a 

 concentric, banded structure. These are of unusual interest. Beginning at the 

 center they have (1) a crystalline or granular core, often showing bright rhombo- 

 hedral cleavage faces; (2) a thin band of clay apparently wanting in some cases; 

 (3) peary white lamellar calcite (Argentine); (4) band of clay; (5) fibrous calcite 

 and (6) outer surface composed of little rhombohedrons. There are several points 

 in the structure of these stalactites deserving special notice. They have not, as 

 yet, been studied microscopically, as is hoped may be done later, but the following 

 facts regarding them are reasonably well ps>tahlished. There is every indication 



