Cxlvi CORRELATION OF MARYLAND MIOCENE 



fourteen per cent of the Alum Bluff s^Decies have survived to the present 

 time. Beyond the Mississippi embayment, though no Miocene beds have 

 been observed outcropping at the surface, the artesian well at Galveston 

 lias penetrated over 1800 feet of strata containing many fossils, evidently 

 of upper Miocene age. This assembly is strongly tinctured with ele- 

 ments characteristic of the Miocene of the Pacific coast which have not 

 survived in the present fauna of the Gulf. These forms are probably 

 the remnant of those cut off from the Pacific waters by the elevation of 

 Middle America in the early Miocene, which for a short time survived 

 on the Gulf side. Owing to these peculiarities there seems no special 

 reason for instituting extended comparisons between the Texas beds 

 and those of Maryland and Virginia. 



We may now proceed to consider somewhat more in detail the relations 

 between the Miocene faunas of Maryland, (1) among themselves, (2) to 

 the Miocene faunas of adjacent States, and (3) lastly to the fauna of 

 the European Miocene. Since the molluscan quota of the fauna is much 

 the largest and that with which the writer is most familiar the local 

 comparisons which are made will be chiefly based upon it." 



The three horizons into which the Maryland Chesapeake has been 

 divided contain altogether about three hundred and sixty-four species 

 of mollusks, of which 14 per cent are peculiar to the Calvert formation, 

 9 per cent to the Choptank formation and 10 per cent to the St. Mary's 

 formation, so that altogether one-third of the molluscan fauna of the 

 Maryland Chesapeake is peculiar to it. Ten per cent survive to the 

 present fauna. Of the whole, one hundred and forty-two species occur 

 in only one of the three subsidiary formations, while two hundred and 

 twenty-two are common to more than one of the three horizons, and 

 quite a number of Calvert species are absent from the Choptank but 

 reappear in the St. Mary's formation. Of those species which are 



*The authors of the systematic lists in this volume have in large part followed in 

 their work the arrangement and determinations made in my Tertiary Fauna of Florida 

 and the collections of the U. S. Geological Survey in the U. S. National Museum. 

 There are naturally some differences due to the use of additional material and to per- 

 sonal equation, which, in the following discussion, will be ignored, as they will in 

 any case hardly affect the percentages. The list as herein contained will be accepted 

 for statistical purposes, except that mere varieties will be left out of consideration ; 

 though on some points I might still hold to my original opinion. 



