278 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1921. 



For the purpose of further elucidation, there are arranged in 

 cases on the east side of the hall several series of the same mate- 

 rials as the last, but in larger sizes, and so far as possible or desir- 

 able in the actual condition in which they were found, the idea being 

 to illustrate by specimens the results of sundry geological processes, 

 as solution and deposition, vulcanism, rock weathering, etc. The 

 descriptive matter below is in part a transcript of labels, interspersed 

 with references to particular specimens. 



LIMESTONE CAVERNS AND ASSOCIATED PHENOMENA. 



The series of objects included in this exhibit are designed to show, 

 either by actual specimens or illustrations, the various stages in the 

 history of a limestone cave. To this end are shown: (1) A theo- 

 retical sketch showing the mode of formation by solvent action of 

 water. (2) Actual plans and sections of caves. (3) Cave interiors; 

 shown by photographs and drawings. (4) As supplementary to the 

 above, a series of cave deposits (stalactites, stalagmites, etc.) (pi. 

 11, fig. 3). These in part are cut and polished to show color and 

 structural variations. (5) The possible economy of caves, shown by 

 blocks of cave marble, nitrous earths, and other salts. (6) Cave 

 life, shown by insects, blind fish, crayfish, bats, etc. (7) The occu- 

 pancy of caves by human beings as temporary dwellings ; shown by 

 illustrations and specimens of bone breccia and implements of 

 human workmanship found in caves. Of particular note in the 

 exhibits are the large stalagmitic and stalactitic forms from Luray, 

 Va., and the complete section, as formed by nature, from the 

 Marengo Cave in Indiana (pi. 11, fig. 2). This bears the following 



legend : 



Section of Marengo Cave. 



Marengo, Indiana. 60,634. 



The stalactites and stalagmites are in their original position 

 as formed in the cave. The longer ones had united at the ends 

 and it was necessary to saw them apart before removing. 

 The smaller stalactites were removed separately, it being 

 found impossible to cut away the material of the roof with the 

 stalactites attached. Hence, while their position is not abso- 

 lutely as formed, it is sufficiently accurate for all practical 

 purposes. The section illustrates a common but easily ex- 

 plained phenomena in caves : That stalactitic growths of con- 

 siderable size are often produced without corresponding 

 stalagmites. The converse of this is also true. The expla- 

 nation is found in the fact that owing to conditions of evapora- 

 tion, all the lime is deposited either before or after dropping 

 from the pendant stalactite, instead of being nearly equally 

 divided between stalactite and stalagmite, as is frequently 

 the case. 



