406 PROCEEDINGS OF THE ACADEMY OF [April, 



THE FOSSIL LAND SHELLS OF BERMUDA.' 



BY ADDISON GULICK. 



Last summer (1903). through advantages offered by the new Bio- 

 logical Station in Bermuda, I was able to collect the shells on which 

 this paper is based. In the stud}^ of the material I owe much to Dr. 

 H. A. Pilsbry, of the Academy of Xatural Sciences of Philadelphia. 



It will be necessaiy in the discussion of the fossils to compare them 

 with the species that are now native, in the looser sense, to the islands. 

 In drawing the line l^etween these and the snails supposed to have 

 been brought by commerce, I shall follow Dr. Pilsbry 's latest paper on 

 the ''Air-breathing ^lollusks of the Bermudas. "^ I shall also rule 

 out all the littoral species, including Truncatella, because the fossil 

 beds were not situated where such shells could be expected. 



The most unsatisfactory feature of work on Bcrmudian fossil land 

 shells is the difficult}' in determining the ages of the various deposits. 

 The rock of Bermuda is exclusively solidified dunes of calcareous sand, 

 and the soil is the rust-colored residue of the weathered rock. In 

 weathering, the surface of the rock becomes completely broken up 

 into pockets and crevices packed with the earth. It is estimated^ 

 that every inch of earth must represent eight or nine feet of rock eroded, 

 and thus when it is possil^le to judge of the average depth of soil formed 

 over a deposit, that depth can be made an index of the age of the 

 deposit. 



Probably the oldest good fossiliferous deposit that I examined is 

 collecting locality No. 807 (see Map No. 3j of the Bermuda Biological 

 Station, at a hard-stone quarry on the west side of Knapton Hill, 

 about midway between Hotel Frascati and "Devil's Hole." At this 

 point a layer of eight or ten inches of red earth containing shells was 

 covered by an ancient dune. The dune has become hard limestone, 

 and its top has been eroded until now the red earth in its pockets must 

 represent a layer averaging not less than six inched in thickness. The 

 series of Poecilozonites that we took from this bed is very incomplete, 

 and the fossils of all the genera are poorly preserved, but notwith- 

 standing this we are able to recognize at least eleven species and sub- 



^ Contributions from the Bermuda Biological Station for Research, No. 2. 



2 Trans. Conn. Acad., Yo\. X. 



3 A. E. Verrill, Trans. Conn. Acad., Vol. XI, p. 490. 



