22 J. W. Dawson—Footprints, etc., on Carboniferous Rocks. 
and others resemble roots, fucoids allied to Buthotrephis, or the 
radiating worm-burrows already referred to. 
Shrinkage cracks are also abundant in some of the Carbonifer- 
ous beds and are sometimes accompanied with impressions of 
rain-drops. When finely reticulated they might be mistaken for 
the venation of leaves, and when complicated with little rill- 
marks tributary to their sides, they precisely resemble the Dic- 
tuolites of Hall from the Medina Sandstone. 
An entirely different kind of shrinkage-crack is that which 
occurs in certain carbonized and flattened plants, and which 
sometimes communicates to them a marvelous resemblance to 
the netted under-surface of an exogenous leaf (fig. 5). Flat- 
tened stems of plants and layers of cortical matter, when car- 
bonized, shrink in such a manner as to produce minute reticu- 
lated cracks. These become filled with mineral matter before 
the coaly substance has been completely consolidated. A fur- 
ther compression occurs, causing the coaly substance to collapse, 
leaving the little veins of harder mineral matter projecting. 
These impress their form upon the clay or shale above and 
below, and thus when the mass is broken open we have a car- 
bonaceous film or thin layer covered with a network of raised 
lines, and corresponding minute depressed lines on the shale 
in contact with it. The reticulations are generally irregular, 
but sometimes they very closely resemble the veins of a reticu- 
lately veined leaf. One of the most ‘curious specimens in my 
possession was collected by Mr. Elder in the Lower Carbon- 
iferous of Horton Bluff. The little veins which form the pro- 
jecting network are in this case white calcite; but at the sur- 
face their projecting edges are blackened with a carbonaceous 
m. 
Slicken-sided bodies, resembling the fossil fruits described by 
Geinitz as Gulielmites, and the objects believed by Fleming and 
Carruthers* to be casts of cavities filled with fluid, abound in 
the shales of the Carboniferous and Devonian. They are, no 
* Journal of Geol. Society, June, 1871. + Ibid, vol. x, p. 14. 
