258 Field Columbian Museum — Geology, Vol. i. 



cave. The form to which I refer is that of which the stalagmite 

 known as "Washington's Monument" (Fig. 4) may serve as a type. 

 It may be described as one which would be produced by piling a 



Fig. 4 — "Washington's Monument," Marengo Cave. 



number of irregular, successively smaller, truncated, inverted cones 

 one above the other. At first'sight this structure appears very regu- 

 lar and suggests rhythmic variations in the supply of matter in the 

 formation of the stalagmite. On close examination, however, it will 

 be seen that the widenings and narrowings are not horizontal, nor do 

 they extend uniformly around. They are rather of the nature of 

 irregular projections and indentations. Such being the case, it 

 seems to me that slight movements of the point of dropping of the 

 water which formed the stalagmite would be sufficient cause for its 

 form. Such variations in direction of growth of a stalagmite are 

 illustrated in a section of one from Robertson's Cave, Springfield, 

 Missouri, shown in Fig. 1, PI. XXXII. Up to a point about one-third 

 of the way to the top, growth was in a direction to the right. Then 

 it turned to the left and then became more nearly vertical. Such 

 variations might especially be expected where no stalactite existed 

 above to maintain the point of dropping in one place, as is the case 



