E.. W. Eilgard—Later Tertiary of the Gulf of Mexico. 61 
any definite data to show the geological features of the region 
beyond the Rio Grande, I call attention to the fact that the 
edge of the Mexican plateau approaches the coast most closely 
to landward of Vera Cruz. At that place, the castle of San 
Juan De Ulloa stands on a rock which, from specimens brought 
home by soldiers from the Mexican war, I then understood to 
be a freshwater limestone, full of helices, or shells resembling 
them. If there be any more definite data extant on this point, 
I should be glad to have them pointed out. It seems almost 
incredible that so obvious a feature of a seaport so frequently 
visited by Americans should not have been better observed, 
even accidentally. 
The casual statements made as to the nature of the rocks by 
travelers, are too indefinite to afford any clue upon which con- 
clusions might safely be based. 
As to Cuba and the rest of the Antilles, we do know that 
their shores are lined with marine fossiliferous Tertiaries, much 
disturbed by the upheavals that have occurred. We even 
have descriptions, and quite a long list Of names, of fossils 
found in these formations. But on the one hand, the English 
the other Tertiaries of the Gulf border. Moreover, the ten- 
dency of most observers to pass lightly over the unconform- 
able, difficult deposits of the Quaternary, in which no glo 
can be gained by describing and naming new species, has left 
us with but a faint idea even as to the presence or absence of 
such beds on the Antilles. I shall therefore not attempt the 
Uunpromising task of a discussion and comparison of what is 
hown of their geology, with the known facts on the main- 
land of the United States. 
How are the latter to be reconciled with the now well-ascer- 
tained great depth of the Yucatan Channel, and the at least 
hot inconsiderable depth of the Straits of Florida? It seems 
scarcely possible to assume that both of these have been 
formed de novo at the end of the Tertiary period; nor even 
that the depth of the Yucatan Channel could have been so 
materially less since the Eocene time, as to allow of the 
freshening of “Sigsbee Deep” by the influx, whether of the 
regular drainage of the Continent, or of the contents of the 
receding great lakes of the plains. But the matter assumes 
