318 FUC01DES IN THE COAL FORMATIONS. 



tion at Point Levy, near Quebec, Canada. Its likeness to our species is rather in the 

 mode of growth than in the form. It has nevertheless an eccentrical expansion of the 

 secondary frond, from a round, linear, apparently tubular stalk, which is sometimes only a 

 bladdery oval tubercle. The fronds themselves, though narrower, deeply dentate on one 

 side, and without arched ribs, have the same general outline as Canlerpites marginatus. 

 Indeed, in comparing the upper part of fig. 7 of Brongniart with fig. 6 of our plate, or fig. 

 8 of Brongniart with our fig. 2, one can but see that these so nearly allied forms are of a 

 same type, and can but be admitted in the same genus.* 



6. GEOLOGICAL HORIZON OF THE LIMESTONE MARKED WITH REMAINS OF CAULER- 

 PITES MARGINATTJS. 



The new species of Caulerpites was found on Slippery Rock Creek, opposite Wurtem- 

 berg, Lawrence County, Pennsylvania, at the base of a hill about three hundred and fifty 

 feet high, abruptly cut down by the erosion of the creek. The succession of the strata 

 thus open to view is seen in the following order, ascending : 



1st. At the low-water level of the river, a bed of soft, black, easily disaggregated shales, 

 intermixed with small oval pebbles of carbonate of iron. At its upper part, the shales 

 pass into a kind of yellowish ball or clay iron ore, their whole thickness varying from five 

 to eight feet here around.f 



2d. They are overlaid by a bed of bituminous, hard splint coal, sometimes shaly, five 

 to twelve inches thick, rarely more, covered by the limestone, with Fucoidal remains, as 

 it has been described above. At Wurtemberg this limestone is one foot thick. In as- 

 cending the creek to about five miles above this place, it continues in view at the base of 

 the hills wherever they are cut by erosion. It preserves the same horizon, is marked by 

 the same species of plants, and its greatest thickness is not over eighteen inches. 



3d. Over the limestone, fifteen feet of soft, grayish shales, without any trace of remains 

 of fossil plants. 



4th. A bed of sandstone, five feet thick, passing sometimes to a hard compound of 

 coarse-grained fire-clay, with leaves and stems of Stigmaria. 



5th. Two feet fire-clay. 



6th. Three feet hard black limestone, of the same appearance and compound as the 

 limestone of the Fucoides, but without remains of plants. 



7th. A succession of thick strata of shales, cut by thin beds of Stigmaria fire-clay and 

 shaly sandstone, with streaks of coal. The shales have an average thickness of one 



* Prof. Brongniart (loc. cit.) compares his fossil plant to some species of Amansice, especially to Aviansiu 

 semijnnnala. Prof. UDger, in his Genera and Species, places it in the genus Sphcerococcites of Sternberg. 



f At some other places, on Beaver River for example, these shales attain a thickness of twenty feet, being 

 cut or underlaid by one or two beds of coal, as in Kentucky. 



