PEELIMINARY REMARKS. XIX 



that of "Cret. N. J." Others mention only the county in which they were 

 found. This condition I find in other collections as well, and it is likely to 

 have been a fruitful source of error. The blame, however, in the case of 

 the Academy of Natural Sciences rests solely with the original collectors 

 and authors of the species; and if some of these errors are continued in 

 the present work from these causes, I do not feel that they could have been 

 avoided. The collections at the Academ)' of Natural Sciences are, never- 

 theless, extremely valuable, as they are largely types of species by Con- 

 rad, Gabb, and Morton. Of the latter, however, there are very few re- 

 maining. 



It will be noticed that very few of the species have been recognized 

 from localities outside of the State It is certainly peculiar that so many 

 local species should have existed within the limits of New Jersey. This 

 may, however, be attributed to certain causes which have existed over these 

 areas during the deposition of these formations, and which would have pro- 

 duced a special fauna fitted for those conditions by eliminating from it all 

 other forms not fitted to withstand them. Beyond this, certain rapid or 

 sudden changes seem to have taken place over nearly the entire coast of 

 this State, at somewhat regular periods, which materially changed the con- 

 ditions of life abruptly. These are recorded in the changes from the green- 

 sand deposit to a siliceous sand deposit between the several layers of marls, 

 in which no animal remains occur. These abrupt changes in conditions 

 and extinction of life over these areas at times also account for the almost 

 entire change of species in the difi'erent beds of marl. But there is still 

 another reason, and perhaps a more direct one, why so few of the species 

 have been identified from other localities than those of the greensand region. 

 This is the condition of preservation of these marl fossils, which are gener- 

 ally only seen as internal casts, and therefore very difficult to identify with 

 perfect shells. But even among the few which have heretofore been cited 

 as common to New Jersey and more southern localities, I find few that will 

 bear critical comparison. For this reason I have been compelled to change 

 the names of several of the species where the types were from those south- 

 ern localities. 



In regard to the identity of the New Jersey beds with the supposed 



