150 
GEOLOGY OF THE FOURTH DISTRICT. 
the porous sandy mass, and only a loose spongy substance remained. This is the second rock 
in the ascending order in which remains of fishes have been found. 
From the researches of Pr f. W. B. Rogers in Virginia, and Prof. II. D. Rogers in Penn¬ 
sylvania, we learn that the Delthyris arenosa and Atrypa elongata are equally abundant in the 
same rock, and one of the distinguishing features of the rock are the cavities resulting from 
the removal of the calcareous matter of the shells. These facts show the wide distribution of 
species over similar beds. It should be remembered also that these fossils so abundant in. 
this arenaceous deposit are often as numerous in almost purely calcareous beds forming the 
termination of the mass. It seems very probable also that the original deposit was more cal¬ 
careous, and that the porous character of the rock may have resulted from the solution and 
removal of calcareous particles. 
The connexion of this rock with those above and below it, is represented in the sections ac¬ 
companying the Onondaga salt group, which show its diminution and final disappearance in 
a westerly direction. 
19. CAUDA-GALLI GRIT. 
Cocktail Grit of Dr. Eights. 
This rock is an argillo-calcareous sandstone, passing into a greenish shale with thin lami¬ 
nae of sandstone and sandy shale. 
A portion of this rock is characterised by the presence of a Fucoides or some analogous 
vegetable form, which when seen in parts, as they frequently are, have a fancied plumose 
appearance, whence, with the lithological character, the name of the rock is derived. 
This rock is not known in the Fourth District, though it is well characterized in the middle 
and eastern parts of New-York and also in New Jersey, as we learn from the Report of Prof. 
Rogers. 
