368 W. H. TWENITOPEL IMl'RESSIONS BY BUBBLES AND RAIN-DROPS 



Impressions made by Bubbles produced from Decay of organic 



Matter 



Bubble impressions formed on the bottom of water bodies by gases ex- 

 pelled from the mud, the gases arising from the decay of organic matter 

 contained therein, will be similar to the impressions made by the bul)bles 

 becoming anchored to the bottom in those cases where the bubbles remain 

 attached to the mud surfaces until the mud ceases to flow. If, however, 

 the bubbles burst from the mud explosively, the effect on its surface will 

 be that of a small explosion, and a conical depression with a slightly ele- 



FlGURE 7. 



-lm2)ressions made hy Bubbles rising through 

 Mud and bursting on the Surface 



vated margin may be formed (figure 7). If the bursting of the bubbles 

 take place while the mud is in a fluid form, no sooner is the depression 

 formed than the mud flows into it, so that it loses any elevation about the 

 margin it may have had and becomes shallower and wider. It appears 

 that, once a bubble has formed a path, others produced near the same 

 point will follow the same course, and as the mud settles to the degree of 

 not flowing, there results a nearly vertical hole which may extend as far 

 down as the source of the bubbles. In holes so made by the writer, they 

 have been found to be open to a depth of two inches from the surface of 

 the mud. Holes of this character resemble those made by worms, and it 

 is possible that some of the vertical worm-holes which have been reported 



