74 
FLORIDA STATE GEOLOGICAL SURVEY. 
less silicified, or when broken up the resulting breccia contains numerous angular 
fragments of chert. 
Iii the north-central part of the peninsula and extending as far 
south as Croom, there are many exposures of chert and cherty lime¬ 
stone which rest on the limestones of the Vicksburg group. This rock 
usually contains many casts and molds of an Echinoid, which Vaughan 
has identified as a Cassidulus. The rock appears to be very persistent 
but seldom attains any great thickness. At Bass Station, about six 
miles southwest of Lake City, it was quarried to a depth of twelve or 
fifteen feet without reaching the underlying Vicksburg group. About 
six miles west of Gainesville on the Newberry road, it appears to 
have a thickness of more than fifteen feet and to rest directly on the 
Ocala limestone, which forms the country rock of that region. The 
same Echinoid is found in cherty beds in many localities between Bass 
Station and High Springs and at Alachua sink, White Springs, Ella- 
ville and Croom. It is also known at various localities in the hard 
rock phosphate region. At the railroad trestle just west of White 
Springs, there is an exposure of sands, marls and clay which is prob¬ 
ably the local equivalent of the limestones belonging to the Hawthorne 
formation. At this locality the beds pass under the Chipola marl 
member. A section at the railroad trestle shows the following ma¬ 
terials : 
1. Sandy loam ..... 20-f- ft. 
2. Soft friable marl containing some bands of chert and numerous 
Echinoids ...... 10-15 ft. 
3. Soft marl containing oyster shells. 
4. Light green thinly laminated siliceous clay. 4 ft. 
5. Light green sand to water... 4+ft. 
Total ...... 44+ ft. 
CHATTAHOOCHEE FORMATION. 
The limestones and marls exposed along the Apalachicola River 
have been grouped in various ways by different writers. In this paper 
the name Chattahoochee formation is restricted to those limestones 
and marls of northern and western Florida which lie stratigraphically 
between the limestones of the Vicksburg group and the Chipola marl 
member of the Alum Bluff formation. Beds of chert occur in this 
formation and thin layers of sand and clay are not uncommon. The 
type locality is at Chattahoochee Landing, where there is an exposure 
of light gray marl and impure limestone. This formation forms 
.Langdon’s 1 Chattahoochee group, and it is apparently the Chatta¬ 
hoochee group of Foerste . 2 
1 Op cit. 
2 Op cit. 
