78 FORMATION OF STALACTITES— MERRILL. vol. xvii. 



upper or lower end, usually the upper, and all growth from the ex- 

 tremity alone ceases, subsequent deposition being wholly exterior, and 

 taking place iu the form of concentric coatings of the carbonate on the 

 outer surface and at the same time from the top. There is thus formed 

 arouud the original tube a compact cylindrical mass, in its typical 

 form constricted at point of attachment but thickening rapidly, aud 

 then tapering gradually into an elongated cone. The material of the 

 stalactite is uot always Avholly carbonate of lime, but in some cases 

 thin intervening coats of iron disulphide are met with; these are rarely 

 more than a millimeter or so in thickness. Such forms have been 

 found in the caverns of Luray, in Virginia. The presence of a mag- 

 uesian carbonate in these deposits has uot been detected in any amount- 

 Through a crystallization which must be nearly contemporaneous with 

 dei)Osition, or at least while the stalactite is still saturated with the 

 carbonated waters, the mass of the material undergoes an arrangement 

 which is sometimes distinctly fibrous (aragonite), the fibers radiating 

 from the center outward, and not infrecpiently being curved downward 

 — that is, curved in such a manner that when the stalactite is broken 

 across it sliows a concave and convex fracture, the concavity being 

 uppermost — toward the top of the stalactite. In other cases the struc- 

 ture is granular throughout, through the development of calcite rhombs. 

 In the stalactites from Weyer's Cave, Shendun, Virginia, the entire 

 center is sometimes occupied by'large (10 mm.) rhombs of clear calcite, 

 from which radiate horizontally elongated forms of the same mineral. 

 It is safe to assume that such crystallizations are wholly secondary. 



It is a natural consequence of their method of deposition that stalac- 

 tites of the type described above are as a rule nearly straight, and hang 

 approximately perpendicularly from the roof. Exceptions to this rule 

 will be noted below. 



In the Wyandotte Cave, and to a less extent in some others, a pecul- 

 iar vermiform stalactite is found which is quite at variance with those 

 described above. They occur in clusters or groups both on the walls 

 and ceiling and are remarkable for their i)eculiar fantastic twistings 

 and turnings, which in extreme cases are almost Medusa-like. Their 

 appearance can best be understood by reference to PI. I, the scale 

 being in inches. This shows a number of detached stalactites both 

 simple and branching. The point of attachment is uppermost in the 

 figures, with but one exception. In order that there be no misunder. 

 standing I have placed the numbers always at the broken end. It w^ill 

 be observed that the processes of deposition already desc^ribed fail to 

 satisfactorily account for these forms, in which the law of gravity 

 seems to have been set at defiance. In fig. 2, it will be noticed, the sta- 

 lactite after growing irregularly downward for about 4 inches turned 

 upward and grew in this direction for half its length, ^o. 3 grew down- 

 ward for an inch or so, and then in a nearly horizontal and upward 

 direction for three or four inches. Number 4 is a singularly contorted 



