INTRODUCTION. 25 



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. Jlvicula, 

 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 it are 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 Corbulw, JVttcw/ce, 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 propriety, perhaps, be called indurated 



