INTRODUCTION. B5 
brown appearance to the whole. The calcareous matter 
of the shells is so much decomposed as to fall to pieces by 
the touch. It is, therefore, almost impossible for a per- 
fect specimen to be removed from its matrix. Avicula, 
Venericardia, Nucula, Venus, Teredo, and a few other 
genera, may be observed in the specimen, and the species 
may be all, so far as made out, referred to those in No. 3, 
and, of course, the stratum be referred to the same epoch. 
In itare fine specimens of the Scutella crustuloides (Morton), 
some of which measure three and a half inches in diame- 
ter. 
** No. 6, is a specimen of the stratum, forty or forty-five 
feet thickness, and called here, ‘ rotten limestone.’ ” 
*“ On this layer of No. 6, is a deposit of sand and 
gravel, mixed with clay, of about twenty feet, through 
which and above the stratum No. 6, break out the Bluff 
springs, of which there are many, say six or eight, along 
the Bluff. In digging wells we find water in about 
twenty feet, in a stratum of white sand and quartz pebbles 
of all sizes, from that of a pea to a pigeon’s egg, of different 
forms, some flat—some round—some elliptical. These 
pebbles are smooth, as if made so by attrition. All the 
water from this Bluff, whether from the springs or the 
wells, is impregnated more or less with carbonate of lime. 
The wells generally more so than the Bluff springs.” 
This specimen was five or six inches square. On frac- 
turing it, obscure casts of Corbule, Nucule, and some other 
bivalves could be identified with some which exist in No. 
3, and the strata between. The casts of a few spiral uni- 
valves were also discernible. A small and very thin 
Pecten, with delicate ribs, seemed to be the only shell 
which left its trace in a calcareous state. On each side of 
the fracture a silvery whiteness marks the deposit of this 
thin and fragile species. The mass of this rock, or as it 
might with more proptiety, perhaps, be called indurated 
D 
