CHESAPEAKE AND COLD WATER MIOCENE. 167 



to the first supposition. There is a well marked CarcUum {chipolanmn 

 n. sp.) in the Chipola marl which simulates in miniature the great 

 Cardiwn magnum of the recent fauna. This is succeeded in the Alum 

 bluff beds by another species extremely similar, but perfectly distinct. 

 This occurs at Oak Grove. Cardium chipolanum is found in Johnson's 

 Hattiesburg phase of the Grand Gulf beds at Roberts, Escambia county, 

 Alabama. At the latter place Professor Smith informs us the sands con- 

 taining the fossils lie directly upon genuine Grand Gulf beds (Johnson's 

 Ellisville phase). If these observations be correct we probably have the 

 Grand Gulf beds (strictly speaking) comprised between the Hawthorne 

 beds below and the Alum bluff beds above, thus making them chrono- 

 logically equivalent to the lower middle portion of the old Miocene 

 rocks of west Florida. The Pascagoula clays of Johnson, formerly 

 associated with the Grand Gulf beds, ma}^ be confidently referred to the 

 newer portion of the newer or Chesapeake Miocene, and would there- 

 fore be separated by a consideral)le time-interval from the typical Grand 

 Gulf rocks. 



There is some reason to believe from fossils collected at De Funiak 

 springs that the Alum bluff beds are represented there, but no question 

 of this sort can be answered permanently without a careful study of the 

 stratigra23hy in combination with an intelligent knowledge of the fauna. 

 Attempts to theorize on the geology of the southern Tertiary from a few 

 imperfectly identified species of fossils and without exact determinations 

 of the stratigraphy are worse than useless, as they multiply error and 

 confusion. 



The Chipola series may be summarized as containing the Chipola 

 marl, the Roberts, Escambia county, Alabama, sands and the Alum bluff 

 beds, which, with the Chattahoochee formation, comprise the subtropical 

 or old Miocene division of the Miocene of the southern and eastern United 

 States. • 



Chesapeake or cold Water Miocene. — Just above the Alum bluff beds in 

 the section A-B, at Alum bluff, lies the gray Chesapeake or newer Mio- 

 cene marl, consisting of an arenaceous greenish gray clay, crammed with 

 fossils. Here the bed is deposited conformably upon the Alum bluff 

 sands, but sharply contrasted with them, both in color and coherence. 

 It reaches here a thickness of 35 feet, which diminishes gradually north- 

 ward to not more than 5 or 6 feet at point C, figure 2. The upper few 

 feet form a zone which is more or less oxidized and has the fossils dis- 

 solved out, owing to seepage of acidified water from the bed above. The 

 fauna of the Chesapeake at Alum bluff includes about 200 species, among 

 which Venus rlleyi, Conns advefsarius, Tnrritella variabilis^ Fasus equalis, 

 Dentalmm atteniiatum, Ecphora quadricostata and Crucibulum constrictum 



