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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 30, 



concave depression. Most of the pits produced by these air-bubbles 

 were different also from rain-prints, in being deeper than they were 

 wide. Their sides were very steep, and often overarching, the cavity 

 below the surface being wider than the opening at the top. The 

 axis of some few of these deeper cavities was oblique to the surface 

 of the mud. Where two bubbles had touched, a vertical thin parting 

 wall of mud was left between them. 



I also exposed the same mud in a soft state to a shower of rain, and 

 reproduced markings like the smaller rain-prints which had been sent 

 me from the Bay of Fundy. By causing single large drops of water 

 to fall from a sponge upon the same mud from a height of about ten 

 feet, circular pits were formed, similar in size and depth to the largest 

 impressions of rain from Kentville, and having similar rims. 

 ^ The occasional discovery of a few isolated cavities of the size of 



rain-prints in ancient strata, seems to have led some geologists to 

 ascribe them to air-bubbles, simply on the assumption that rain would 

 cause the mud or sand to be pitted all over by numerous impressions. 

 But, if the hollows have characters proper in other respects to rain- 

 prints, we ought not to seek for a distinct cause, even although only 

 one or two may appear on a wide area. I saw such isolated cavities, 

 which I feel sure were due to the fall of drops of water, on dried mud 

 on the beach at Baltimore in 1842, and brought away with me a solid 

 specimen. A few heavy drops from a thunder-shower, which had 

 spent its force elsewhere, may have caused them ; or one of the nume- 

 rous water-birds which were flying about the shore may have let fall 

 a drop of salt-water from its wing, or from a fish which it was carry- 

 ing off in its mouth. 



Triassic Rain-prints. 



I have alluded to my visit to the quarries of New Red Sandstone or 

 Trias at Newark, in New Jersey, in 1841, where rain-prints occur, 

 and to still finer examples observed by Mr. Redfield in the same 

 formation at Pompton, in New Jersey. In that locality many of the 

 layers of red shale or red clay are ripple-marked and traversed by 

 shrinkage-cracks, and exhibit the foot-prints of tridactylous birds, so 

 common in the shale and sandstone of the valley of the Connecticut. 

 In their average size these ancient rain-prints agree with those of 

 modern date, although none of them equal the largest of those, before 

 mentioned, from the Bay of Fundy. As in specimens of recent mud 

 from Kentville, the triassic strata exhibit every gradation from trans- 

 ient rain, where a moderate number of drops are well preserved (see 

 fig. 2), to a pelting shower, which by its continuance has almost ob- 

 literated the circular form of the cavities. In the more perfectly pre- 

 served examples, smaller drops are often seen to have fallen into 

 cavities previously made by larger ones, and to have modified their 

 shape. In some cases of partial interference, the last drop has obli- 

 terated part of the annular margin of a former one; but in others it 

 has not done so, for the two circles are seen to intersect each other. 

 Most of the impressions are elliptical, having their more prominent 

 rims at the deeper end. We often see on the under side of some of 



