200 Scientific Geology. 



" vegetable earth," in which, 20 feet from the surface, was found " a 

 large fallen oak (?) tree." Next a stratum of tough blue clay, six 

 inches thick ; next strata of " iron ore, or gravel impregnated with 

 it : " " below this, lay the shells, &c. in apparently fresh marsh mud." 

 (green sand?) Here were found a very perfect shark's tooth, (Plate 

 XIII. Fig. 37,) the cast of a small species of Venus, (Fig. 40,) and 

 the same species of Turbo as occurs at Gay Head. (Plate XII. Fig. 

 4.) Mr. Kent took the trouble of having a shaft sank on the margin 

 of the swamp in the vicinity of this well, and the strata penetrated, 

 correspond with those mentioned above. The water rushing into the 

 opening, however, prevented him from examining thoroughly for pet- 

 rifactions. 



Another well was opened 10 years ago, 80 rods nearer the sea 

 than the first mentioned, and at a lower level. After digging 13 feet, 

 through strata similar to those in the first well, they came to a solid 

 layer of ferruginous sand stone, which arrested their progress. 

 " Angry with disappointment," said the owner of the well, " my man 

 brought a thundering blow upon the rock, and through it went ; and 

 up spouted the water. We then cleared away and found a plate of 

 iron (ore) about two inches thick : under this plate lay a bed of strong 

 marsh mud, full of cohogs and clams, and cockles, about two bushels 

 of which we took out. In the center lay plainly a land animal's 

 bone, as large as my wrist, and six inches long, fractured, which was 

 given to some Society in- Boston." This fine collection has nearly 

 disappeared. Mr. Kent, however, sent me a single specimen, a cast 

 of a Venus, much abraded, not to be distinguished in size and shape 

 from that sketched on Plate XII. Fig. 3. The mineralizer in this 

 case is clay ; not so much indurated but that it may be cut without 

 difficulty. And this is the case with all the Duxbury specimens, ex- 

 cept the shark's tooth, which is not mineralized, or only partially so. 

 In the specimen from the second well mentioned above, in the cavity 

 occupied by the hinge, is a small quantity of green sand, exactly like 

 that at Gay Head ; which proves satisfactorily the identity of the 

 marsh mud and the green sand : and that the green sand of Gay 

 Head is identical with that in England, a comparison of specimens 

 shows. 



Thus it appears that the proof is as strong as could be desired, of 

 the entire similarity between the plastic clay of Gay Head, and the 

 fossiliferous formation above described, at Duxbury. True, no varie- 

 gated clays are mentioned at Duxbury : nor, if I rightly recollect, do 



