MUSEUM OF COMPARATIVE ZOOLOGY. 91 



plants. In part it is covered by a growth of lichens, and in part alto- 

 gether bare of vegetation. 



This assemblage of facts makes it seem clear that the locality whence 

 this Cretaceous material is derived is not more than a few hundred feet 

 to the north of the site where these fossils are found. Were it farther 

 away, there could be no such concentration of the Cretaceous waste. 

 The hypogene material would be more extensive than it is. I have 

 therefore no hesitation in saying that we have in this immediate vicinity 

 a deposit of Cretaceous age. It is probable that this deposit of small 

 area is girdled about by strata of the same age as those about Gay 

 Head. This is indicated by the fact, that, at various points in every 

 compass direction from this locality, the drift contains large amounts of 

 bright-colored clays such as give the name to Gay Head. These clays 

 are not seen in their natural position, but are commingled with the 

 glacial waste, the fact being that when the glacier overrode this area it 

 ground up and commingled a good deal of bed-rock clays over which it 

 moved with the morainal material brought from a distance. A careful 

 study of all the exposures on Martha's Vineyard containing Tertiary 

 clays has failed to show any distinct fragments of Cretaceous rock. This 

 assemblage of facts has led me to the conjecture that some small remnant 

 of the Cretaceous beds projecting through the enveloping clays of later 

 age is the source whence these fragments containing fossils have been 

 derived. 



The foregoing conjecture is more probable, for the reason that it will 

 explain in a satisfactory way the origin of much of the sedimentary 

 matter contained in the beds of the Gay Head section. That section is 

 remarkable for the very large amounts of siliceous matter contained in 

 its sandy and pebbly beds. This material is substantially what would 

 be obtained from the erosion of the Cretaceous strata such as are found 

 at this point, and the reassortment of the materials. 



The physical conditions of the fragments of Cretaceous rock appear to 

 indicate that the beds were deposited near a shore line. The rock is of 

 a very coarse texture, showing faint indications of cross bedding ; the 

 clay element is scanty, and the quantity of lime is very small. It is 

 evident that the bed containing the fossils was accumulated with con- 

 siderable rapidity, and that only in certain levels was the. organic life 

 developed in sufficient quantity to make the bed fossiliferous. All these 

 conditions indicate that the deposit was formed near the coast line. 



This opinion is borne out by the character of the fossils. The great 

 prevalence of oysters, and the fact that the two valves are generally 



