The Carrizo Sands. 
53 
the Cretaceous, the Lignitic and Midway both being entirely ab- 
sent. In all this territory the Carrizo sands have a wide develop- 
ment and form the body of many of the hills. 
Along the Rio Grande the upper margin of the Carrizo sands is 
found just below the mouth of Espada creek, where the ripple marked 
micaceous sands with iron concretions which mark its culmination, 
are conformably overlain by the lignite bearing sands and green- 
ish clays, carrying palmetto leaves and other fossil plants, which 
here form the base of the Marine beds and grade upward into beds 
containing the Marine fossils which distinguish that substage fur- 
ther east. 
We have therefore in the Carrizo sands, as devloped on the Rio 
Grande, a series of sands of very different character from the earlier 
deposits which make up the Midway and Lignitic or Lower Eocene, 
and which rests unconformably upon them. Its materials are more 
nearly those of the succeeding Marine beds, with which it is appar- 
ently in conformity. 
From these facts it will be seen that the Carrizo sands are not a 
part of the Lignitic, as formerly supposed, but that in reality they 
correspond both in position and composition with the Buhrstone of 
the Alabama section, of which we therefore consider them the equiva- 
lent, and form the base of the, Claiborne series or the Middle Eocene. 
m 
