258 FIELD CoLUMBIAN MusEUM—GEOLOGY, VOL. 1. 
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 

Fic. 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, Pl. XXXII. Uptoa 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 
