ON THE FOKMATION OF STALACTITES AND GYPSUM IN- 

 CliUSTATIONS IN CAVES. 



By George P. Merrill, 



Curator of the Ihparimcnt of Gvoloi/y. 



During the season of 1893 work in connection with the World's 

 Columbian Exposition took the writer into a considerable number of 

 the limestone caverns of the eastern United States and afforded him 

 opportunity for observations regarding the methods of formation of the 

 interesting- deposits noted in the title. The results of these observa- 

 tions are given herewith, it having seemed to me that, while no new 

 principle is involved, the subject as a whole has not received all the 

 attention it deserves. 



Stalactites. — The manner in which the carbonate of lime in the form 

 known as stalactite and stalagmite is deposited is, in brief, as below: 

 Water filtering- through the roof of a limestone cavern, is, in virtue of 

 the carbonic acid it contains, enabled to dissolve a small amount of the 

 lime carbonate, which, is again deposited when the excess of carbonic 

 acid escapes either through relief from pressure or the evaporation of 

 the water. Conditions fixvorable to either process are furnished by the 

 water filtering- through the roof and dripping' slowly to the floor be- 

 neath. In cases where the Avater filters sufficiently slowly, or evapo- 

 oration is correspondingly rapid, the deposit of lime carbonate from the 

 roof takes at first the form of a ring around the outer portion of the 

 drop, a natural consequence of the evaporation of a suspended drop of 

 liquid, as may readily be shown by laboratory experiments. This 

 process may go on until the ring becomes prolonged into an elongated 

 cylinder, or tube, the diameter of which may not exceed five milli- 

 meters, though usually ranging from five to ten, and of all lengths up 

 to 50 cm. In exceptional cases this length may be exceeded, but 

 owing to the delicacy of the material, the stalactite usually breaks of 

 its own weight and falls to the floor before a length of even 100 or 

 150 mm. is reached, to become imbedded in the stalagmitic material 

 there forming. Lengths of even these dimensions are comparatively 

 rare for the reason that the tube becomes shortly closed, either at its 



Proceedings National Museum, Vol. XVII — No. 985. 



77 



