314 FUCOIDES IN THE COAL FORMATIONS. 



terials of which the coal is a compound, or immediately over them. For they appear to 

 derive the black color, which seemingly paints them on the limestone, rather from the 

 coal than from their own substance. When some detached blocks of the limestone have 

 fallen into the creek, and, washed for a time, have been cleared of the coal which adheres 

 to the lower surface, the matter becomes bleached, and the remains "of Fucoides appear in 

 slightly depressed and dark distinct outlines. But when the coal, which adheres to the 

 limestone as if it was strongly glued to it, is removed by mechanical force, the stone 

 preserves its black color, and the remains of these plants are scarcely discernible. On 

 the line of contact with the coal and for one or two inches above it, the limestone, whose 

 thickness varies from twelve to eighteen inches, is somewhat shaly, though of a piece, and 

 homogeneous. It is a kind of black band, containing sulphur and iron in large propor- 

 tions, and essentially composed of broken remains of innumerable marine shells. Though 

 hard, compact, and in banks generally continuous, it breaks into large cuboidal pieces. 

 The Fucoides, which occupy only a few inches of the lower and shaly part of this lime- 

 stone, are mixed with the remains of shells, and often perforated and lacerated by them. 



3. NAME AND DESCRIPTION OF THE PLANTS. 



Caulerpiies marginatum, spec, nov., is the name of these Fucoidal remains. Their form, 

 however variable,* may be compared to that of a lyre or harp. From a horizontal base, 

 the margins, at first nearly parallel, slightly diverge in ascending, and then unite into a 

 rounded top, as in fig. 2. Or the outer margin, diverging more in ascending from the 

 base, becomes more extended than the other, and is once or twice broadly lobed or only 

 wavy, as in fig. 3. The fronds vary in length from two inches to one foot, are half as 

 broad as long, and surrounded by an apparently fleshy or tubular margin from one-eighth 

 to one-fourth of an inch broad. Strongly arched ribs, apparently produced by alternate 

 inflation and thinning of substance, pass from the inner side of the rim to the other 

 border, filling the whole lamina. These arched lines look somewhat like the forking or 

 dichotomous thickened veins of some Gyclopteris of the coal. But they are not true 

 nerves, for they do not regularly branch or connect with each other. They abruptly vary 

 in thickness or change their general direction, even crossing each other in various ways. 

 This last appearance is likely caused by compression of a body somewhat inflated like a 

 bladder. The ribs, thin and narrow at and near the margin of the frond, are enlarged in 

 the middle. They seem to be produced by such a spongy network of anastomosing fila- 

 ments, as is seen in some of our living Algae, which serves especially to strengthen the 

 structure of the plants. The base of the fronds, abruptly and nearly horizontally cut, is 

 joined at one of its corners, generally more acute than the other, to a stalk or stipe, per- 



* See plate 1. 



