﻿1851.] 



LYELL ON RAIN-PRINTS. 



241 



and all the deep ends have the same direction, showing towards which 

 quarter the wind was blowing. Two or more drops are sometimes 

 seen to have interfered with each other ; in which case it^is usually 

 possible to determine which drop fell last, its rim being unbroken. 



On some of the specimens the winding tubular tracks of worms are 

 seen, which have been bored just beneath the surface (see fig. 1). 

 They occasionally pass under the middle of a rain-mark, having been 

 formed subsequently. Sometimes the worms have dived beneath the 

 surface, and then reappeared. Occasionally the same mud is tra- 

 versed by the foot-prints of birds (Tringa minuta) and of musk-rats, 

 mink, dogs, sheep, and cats. The leaves also of the elm, maple, and 

 oak trees have been scattered by the winds over the soft mud, and, 

 having been buried under the deposits of succeeding tides, are found 

 on dividing the layers. When the leaves themselves are removed, * 

 very faithful impressions, not only of their outline, but of the minutest 

 veins, are left imprinted on the clay. 



On one specimen of dried mud from Kentville I observed numerous 

 small protuberances which on a hasty view seemed not unlike the 

 casts of rain, but which I satisfied myself could not be such, because 

 they stood out in relief from the upper surface of the mud, on which 

 foot-marks of birds were indented. On examining this slab more 

 closely, the protuberances were seen to be irregular in form, and be- 

 neath them were found small pellets of shale and crystals of salt, which 

 had evidently lain on the beach, and then been covered with a film 

 of sediment. This solid matter not having shrunk when the muddy 

 layer dried in the sun, a small projection was caused. Small cracks 

 were usually visible round the base of each of these protuberances. 



Another set of small convexities, also protruding from the upper 

 surface of the mud, proved to be the crusts of small cavities, each 

 cracked at the top, and were suspected by Mr. Faraday, to whom I 

 showed them, to be bubbles of mud which had dried without bursting. 

 He succeeded in producing similar convex protuberances experimen- 

 tally, by pounding up the Kentville mud, moistening it with water, 

 and then, by means of glass tubes, introducing air below, which rose 

 to the top in bubbles. Some of these being dried, consolidated with- 

 out breaking, until finally the crust which covered the cavity where 

 the air had been imprisoned, cracked at the top on shrinking, like the 

 convex protuberances from the Bay of Fundy. 



Being desirous of ascertaining whether air-bubbles, rising through 

 mud and bursting as they reached the surface, could give rise to cavi- 

 ties similar to those caused by the fall of rain, I poured some pounded 

 mud from Kentville on a small quantity of water, and shook the basin 

 containing it, upon which numerous bubbles of entangled air rose 

 through the mud, and, on bursting at the surface, left cavities re- 

 sembling in size the ordinary rain-prints from Nova Scotia, but very 

 different in character. Nearly all of them were perfectly circular, 

 with a very sharp edge, and without any rim projecting above the 

 general surface. In a few cases, however, there was a slight, narrow 

 rim, sharper and more even than that of a rain-print. In no instance 

 was this rim connected with a greater depression at one end of an oval 



