﻿1851.] 



LYELL ON RAIN-PRINTS. 



239 



birds, shrinkage-cracks are seen, together with fossil impressions and 

 casts of rain-drops and of hail. 



Early in the present year I received from Mr. Richard Brown some 

 fine specimens of rain-marks from the greenish shales of the coal- 

 measures of Cape Breton, Nova Scotia, to which he has made a passing 

 allusion in his excellent description of the Sydney coal-field in our 

 Quarterly Journal*. A comparison of all these specimens has con- 

 vinced me that the impressions of triassic and carboniferous date, above 

 mentioned, have been correctly referred to the action of rain, and that 

 they are distinguishable from such cavities as are sometimes made by 

 the rising of air-bubbles through mud or sand, with which Mr. Desor, 

 in a memoir recently published, has declared many, if not all, the 

 supposed fossil rain-marks to have been confounded |. 



Recent Rain-prints of the Bay of Fundi/. 



In my 'Travels in North America' J some notice is taken of the 

 peculiar combination of circumstances which render the mud-flats, 

 exposed at low-tide in the Bay of Fundy, so peculiarly fitted to receive 

 and retain the foot-prints of animals, or any impressions which may 

 happen to be made on their surface. The sediment with which the 

 waters are charged is extremely fine, being derived from the destruc- 

 tion of cliffs of red sandstone and shale, belonging chiefly to the coal- 

 measures. On the borders even of the smallest estuaries communica- 

 ting with a bay, in which the tides rise sixty feet and upwards, large 

 areas are laid dry for nearly a fortnight between the spring and neap 

 tides, and the mud is then baked in summer by a hot sun, so that it 

 solidifies and becomes traversed by cracks, caused by shrinkage. 

 Portions of the hardened mud may then be taken up and removed 

 without injury. On examining the edges of each slab, we observe 

 numerous layers, formed by successive tides, usually very thin, some- 

 times only one-tenth of an inch thick, — of unequal thickness, however, 

 because, according to Dr. Webster, the night-tides, rising a foot higher 

 than the day-tides, throw down more sediment. When a shower of 

 rain falls, the highest portion of the mud-covered flat is usually too 

 hard to receive any impressions ; while that recently uncovered by 

 the tide near the water's edge is too soft. Between these areas a zone 

 occurs, almost as smooth and even as a looking-glass, on which every 

 drop forms a cavity of circular or oval form, and, if the shower be 

 transient, these pits retain their shape permanently, being dried by 

 the sun, and being then too firm to be effaced by the action of the 

 succeeding tide, which deposits upon them a new layer of mud. 

 Hence we often find, on splitting open a slab an inch or more thick, 

 on the upper surface of which the marks of recent rain occur, that an 

 inferior layer, deposited perhaps ten or fourteen tides previously, 

 exhibits on its under side perfect casts of rain-prints, which stand out 

 in relief, the moulds of the same being seen on the layer below. But 

 in some cases, especially in the more sandy layers, the markings have 



* Vol. vi. p. 119. f Edinb. New Phil. Journ. for 1850, p. 246. 



t Vol. ii. p. 126. 



