262 FieELD CoLuMBIAN MusEuM—GEOLOGY, VOL. I. 
ing, in the lapse of years, some data on this point Mr. S. M. Stewart, . 
manager of the cave, kindly allowed, at my request, several stalac- 4 
tites and one stalagmite to. be marked by Mr. Claude Stroud, who ~ 
lives near the cave, and who, by keeping watch of their growth, can | 
note any variations which they undergo. It will be understood, how- ~ 
ever, that the rate of growth is so slow that it is not likely that before ~ 
the end of ten years at least any appreciable change will have taken 
place. The record of the stalactites marked is as follows: 

No. 1 Near ‘Tower of Babel,” Drops at intervals of 344 minutes. 
No. 2 In “Queen's Palace,” a, - = “ 45 seconds. 
NOs aT u ¢ “ 216 times per minute. 
These are simple stalactite tubes. 
The stalagmite marked is in ‘‘Crystal Palace Gallery,” and 
receives eighteen drops a minute. 
SHILOH CAVE. 

ERODED StaLactites.—The stalactite shown in Fig. 7, occurring 
near the southern end of the cave, furnishes an interesting illustra- 
tion of the fact that cave waters may vary in their action from forma- 
tive to erosive, according to the quantity of carbonate of lime they 
contain. ‘Thus, in the case of the stalactite here represented, the 
waters flowing over the limestone shelf to which it is attached had at 
one time built it up to the general form shown. Later, however, 
the character of the waters changed and they began to erode, as shown 
by the pits on the surface, the very mass they had previously built 
up. ‘These processes of deposition and erosion are, of course, going 
on side by side in nearly all limestone caves, but it is not often that 
erosion follows so rapidly after deposition. Many smaller stalactites 
in other parts of the cave show similar erosion. 
Lear Stacactites.—Many of the stalactites of this cave are leaf- 
like in their form so far as this may describe a broad, thin and 
pointed shape. Often the appearance is that of a series of ovate 
leaves folded along their midribs and hanging down from a project- 
ing ledge. The ‘‘leaves” of one such projecting mass are nearly | 
six feet in length, and the weight of the mass must be several thou- 
sand pounds. It is remarkable that such a weight can be sustained 
