.1912.] STEVENSON— THE FORMATION OF COAL BEDS. 473 



The sandstone, in thin flags used for paving, is divided by laminae 

 of unctuous clay, which received and retained the impressions. 

 Twenty-three footprints were obtained, all of them on the under 

 surface of slabs, casts in relief of impressions made upon the clay. 

 There were also casts of shrinkage cracks in the clay, made after 

 the footprints were formed. Rain prints were observed on the 

 slabs which Lyell took to England. 



The sandstones in other coal fields have similar markings ; 

 Ashley has described ripple-marked sandstones in Indiana and J. A. 

 Udden has found them in Illinois. Dawson, ^^ who recognized the 

 importance of recording all observations, has noted the occurrence 

 of ripple and rain marks as well as of footprints at many localities 

 within the Acadian areas. A sandstone in South Joggins shows 

 distinct rain and footprints ; on the shore of Northumberland 

 strait, where the strike coincides with direction of the shore, great 

 surfaces are exposed with ripple marks and worm trails. In 1842, 

 he found, near Tatamagouche, footprints on a rippled surface and 

 in 1843 ^""c discovered two other series of prints, one of which was 

 somewhat defaced by rain marks. Alany beds within this region 

 have ripples, rain marks, worm trails and sun cracks in clay laminae 

 within the sandstones. Lyell summarized the information respect- 

 ing them. Hull has recorded similar conditions in Lancashire of 

 England and Miller has described the footprints at Dalkeith in 

 Scotland.^- Similar markings are reported from almost all the 

 large coal areas, and they are characteristic of sandstones contain- 

 ing laminae of clay on which the markings were impressed. 



Alany authors have noted the " Vegetable soils " or " Ancient 

 soils " observed in sandstone. These may be marked by local 

 deposits of coal or by erect trees in situ, with or without traces 

 of coal around the roots. 



^^ J. W. Dawson, " Acadian Geology," 2d ed., 1868, pp. 167, 215, 217, 325, 

 328, 355, 357, 410; Supplement, 1878, pp. 62, 64. 



°^ C. Lyell, " On Fossil Rainmarks of the Recent, Triassic and Carbon- 

 iferous Periods," Quart. Journ. Geol. Soc, Vol. VIL, p. 244; E. Hull, 

 " Geology of the Country around Wigan," 2d ed., Mem. Geol. Surv. Great 

 Britain, 1862, pp. 9, 10. 



