54 IOWA ACADEMY OF SCIENCES. 



that the crystalline core was once fibrous, but this structure has mostly disap- 

 peared, especially in the larger stalactites and the rhoiubohedral cleavage has 

 replaced it. In the smaller forms the transition from the radiating fibrous condi- 

 tion to the crystalline aggregate of rhombohedrons can be traced; the long acicu- 

 lar crystals become less distinct, but traces of them can still be seen after the rhora- 

 bohedral form makes its appearance. Recrystallization has taken place and the 

 particles have rearranged themselves to conform with the interior structure of the 

 rhombohedrons; in other words, they are identical with the crystal form of the 

 latter in all but external outline, and this has been prevented from developing, 

 showing itself only on cleavage faces. A strong indication that this granular core 

 was once fibrous is the fact that this is the common structure found in all these 

 caves. The small forms all show the fibers, but as they increase in size alteration 

 has taken place. 



Another point of interest about these stalactites is the band of pearly, lamellar 

 calcites occurring between the granular, crystalline core and the fibrous external 

 layer. These white, undulating lamellae form concentric rings in marked contrast 

 to the radiating fibers associated with them. Occurring on both sides of the Argen- 

 tine there is in most cases, if not in all, a thin band of clay. It is this that has 

 doubtless slopped deposition for a time and the different variety was formed on 

 account of the changed conditions. 



The rhombohedrons forming the outer surface, while the interior is still formed 

 of the radiating fibers, also deserve more than passing notice. They occur on the 

 larger stalactites, not on the delicate branch-like forms. The outer surface of the 

 latter owes its silky lustre to the innumerable fibers composing the surface. These 

 frequently form delicate, cotton-like masses covering the outside of the satin spar. 

 But on the majority of the stalactites occur the crystal aggregate of rhombohe- 

 drons. These may have have been deposited after the radiated interior was 

 formed, but they seem to be due, rather, to the alteration or recrystallization of 

 the fibrous mass, as in the case of the granular core. The conditions under which 

 the fibers were formed have changed and there has been a corresponding altera- 

 tion in the crystalline condition of the calcite. 



If not the most interesting to the mineralogist, the white satin spar 

 occurring in the large branch-like clusters is at least notable on account of 

 its great beauty and rarity. It is difficult to give any idea of the rare and 

 delicate appearance of these masses as they hang suspended from the roof 

 of the caverns. At a distance they resemble white branching coral as much 

 as anything. But near at hand the twisted and gnarled stems vpith their 

 beautiful silky luster bear no resemblance to coral. The peculiar shapes 

 assumed by these forms, differing so much from the ordinary stalactites, 

 are no doubt due to the air currents moving through these passages. The 

 wind coming now from one direction, now from another, causes the dx'ops 

 holding the lime in solution to be blown to one side and another of the 

 slowly growing stem, the drop being held by the surface tension. The 

 water does not trickle down undisturbed, as when forming the long straight 

 stalactites depositing an even layer on the end and sides, but the carbonate 

 is deposited for a time on one side of the branch and then, later, on 

 another side. These clusters are extremely delicate and are removed with 

 difficulty from the rock to which they are attached. 



In these caves are found many large and fine stalactites and stalagmites. 

 Some are short and stumpy, others long and slender. In one small opening 



