30 THE EOCEXE DEPOSITS OF MAEYLAXD 



described a number of new species. About this time Henry C. Lea pub- 

 lished a " Catalogue of the Tertiary Testacea of the United States/' in 

 which the Middle Atlantic Slope forms are included. 



Subsequent to 1850 interest in the Tertiary geology of the Middle 

 Atlantic Slope seems for a time to have waned, and during the next 

 twenty-five years very few investigations were carried on within the dis- 

 trict. In Maryland two surveys, partly of a geological but more largely 

 of an agricultural nature, were inaugurated, the first, under James Hig- 

 gins, producing six reports between 1850 and 1858, and the second 

 under Philip T. Tyson, who presented two reports in 1860 and 1863. 

 In the report for 1860 the Tertiary is described in some detail, although 

 no attempt is made to establish the limits of its several divisions. 



Conrad continued, however, to carry on his investigations upon the 

 Atlantic Tertiary belt, adding to the number of new fossil forms and 

 publishing two catalogues of species. 



During the last twenty-five years, and particularly in the latter part 

 of this period, many more contributions have been made to the geology 

 of the Middle Atlantic Slope. Among those who have given the subject 

 attention may be mentioned McGee, Heilprin, Darton, Uhler, Shattuck, 

 Bibbins, Harris and the authors of this report. To the publications of 

 McGee we are indebted more than to any other for a general statement 

 of Coastal Plain conditions. Although some modifications have been 

 deemed necessary after a detailed study of the formations, the writers 

 are impressed, from a careful examination of large portions of the area, 

 with the general correctness of the broad principles enunciated by him. 

 Heilprin has devoted considerable attention to Atlantic Coast paleon- 

 tology, comparing several of the Eocene species of Maryland and Vir- 

 ginia with European forms, and correlating the strata, as a result of 

 these investigations, Avith the lower members of the English and French 

 series. Both Darton and Uhler have studied the local relations of the 

 Eocene deposits, the former having prepared several United States Geo- 

 logical Survey atlas sheets of the central and southern portions of the 

 district. 



Others have turned their attention from time to time to the area, and 

 from their knowledge of other districts have aided to a greater or less 



