MARYLAND GEOLOGICAL SURVEY 45 



The Tertiary Formations. 



The only formations belonging to the Tertiary in Cecil county are 

 the Aquia, which is Eocene, and possibly the Lafayette, which is re- 

 ferred provisionally to the Pliocene. As far back as 1830, Conrad 

 had discovered and described a few Eocene forms from Southern 

 Maryland, and the formations which carried them at Eort Washing- 

 ton he had referred to the " London Clay." Three years later, Isaac 

 Lea published his " Contribution to Geology," in which for the first 

 time the term " Eocene " was applied to the lower portion of the 

 Tertiary deposits. All this work, however, was carried on well out- 

 side the limits of Cecil county. After the year 1850, there was little 

 done in the Tertiary geology of Maryland for 25 years. When work 

 was once more resumed, Heilprin took an active part in the discussion 

 by his contributions to the Eocene paleontology and by his correla- 

 tion of the Eocene deposits of Maryland and Virginia with horizons 

 in Europe. Darton traced the Eocene northward under the name 

 of Pamunkey, and in 1890 announced its presence along the northern 

 bank of the Sassafras river. Six years later, Professor Clark brought 

 out an extensive monograph on the Eocene deposits of the Middle 

 Atlantic Slope, in which he noted the presence of Eocene along the 

 northern bank of the Sassafras river, and described at great length 

 the paleontology of the Eocene as developed in Maryland, Delaware 

 and Virginia. In 1901, Clark and Martin published an exhaustive re- 

 port on the Eocene deposits of Maryland. In this paper the Eocene 

 is subdivided into the Nanjemoy and Aquia formations, and the latter 

 is indicated as present along the northern bank of the Sassafras river 

 in Cecil county. 



The separation of the Lafayette formation in Cecil county was also 

 going forward while the Eocene stratigraphy was being studied. 

 McGee, in 1888, announced the Appomattox formation as extending 

 from Virginia to the Potomac river, and in 1891 Darton announced 

 the continuation of this formation northward across Maryland, and 

 mapped it as developed in isolated patches along the eastern margin of 

 the Piedmont Plateau and also occupying portions of the Coastal 

 Plain from the Potomac river to the head of Chesapeake Bay. A 



