﻿244 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 30, 



longing to the genus Ischypterus, Egerton, are found in the red sand- 

 stone at Pompton. 



As some geologists imagine that a great part of the impressions, 

 imputed to rain, may have been simply the effect of air-bubbles rising 

 through mud, I may state that I agree with Mr. Redfield in thinking 

 that, in such examples as those above-described, no practised observer 

 can fall into a mistake. The oval form of so many of the cavities, 

 and their greater depth at one end, are characters alone sufficient to 

 prove the real origin of the imprints on the Pompton shales. It has 

 indeed been objected that where triassic shales alternate with quartz- 

 ose sandstones, as at Storeton Hill, on the Mersey, near Liverpool (a 

 spot which I have myself visited), we might have expected the rain- 

 marks to have been more blunted by a current of water having ex- 

 erted sufficient power to spread grains of sand over a large surface of 

 mud. Mr. Cunningham gave an answer by anticipation to this ob- 

 jection, by suggesting that the fine sand of the white quartzose sand- 

 stone, in which the casts of rain-prints are preserved, may have been 

 blown by the wind over an area which we may infer to have been above 

 water at the time, because of the depth of the Cheirotherian foot- 

 prints traversing the rain-marked layers. I have noticed in my 

 ' Travels in North America,' that on the beach at Beauly, in the delta 

 of the Savannah river, in Georgia, I saw numerous foot-tracks of ra- 

 coons and opossums made on the sandy mud, where the animals had 

 come down to the sea-shore to feed on oysters. These trails had been 

 formed during the four preceding hours or after the ebbing of the 

 tide. The surface of the mud had, by exposure to the air and sun, 

 already acquired in that short time a considerable degree of firm- 

 ness and consistency, and, while some of the moulds remained empty, 

 others were half-filled with fine blown sand, which had already quite 

 covered up a portion of each trail. The quartzose sand was in this 

 instance derived from a low cliff, formed of tertiary strata so incohe- 

 rent that clouds of minute grains were swept along by a gentle wind, 

 — admirably exemplifying a process by which perfect casts of foot- 

 marks or of rain may be taken in a matrix capable of being afterwards 

 converted into the hardest quartzose sandstone' 1 '. 



Carboniferous Rain-prints. 



In the sixth volume of the Quarterly Journal of the Geological 

 Society, Mr. Richard Brown communicated to us an accurate and 

 detailed account of the Sydney coal-field in Cape Breton, Nova Scotia. 

 In that paper he called our attention to the occurrence in the coal- 

 measures of thirty underclays with Stigmaria, and eighteen examples, 

 at different levels, of the fossil trunks of trees standing erect, or per- 

 pendicular to the inclined planes of stratification, the greater part of 

 the trees having their roots attached. Together with these proofs of 

 the existence of forest-covered land on that area at different periods 

 during the accumulation of the coal, he has described several inter- 

 calated strata of a marine or brackish-water character. We are pre- 



* Travels, vol. i. p. 166. 



