SECOND ANNUAL REPORT—STRATIGRAPHIC GEOLOGY. 
71 
thicknesses, according to Dali, 1 consists of greenish clay seventy feet, 
ferruginous yellow sandstone four feet and phosphate rock twenty 
feet. The maximum thickness of the Hawthorne formation, as given 
by the same author, is 125 feet. 2 However, over a large part of the 
peninsula, where the sole representative of the Hawthorne formation 
is the phosphatic or siliceous rock, the thickness is but a few feet. 
Physiographic Expression:— The Hawthorne formation seldom 
has much influence upon the surface configuration in the region which 
it underlies. Locally, however, the cherty beds protect the underlying 
rock from erosion and thus give rise to ridges; and where the clays 
lie near the surface they are characterized by an erosion surface of 
moderate relief. The chert-capped ridges are usually inconspicuous, 
but in some parts of the phosphate region they are sufficiently marked 
to form well defined topographic features. 
Paleontologic Character:—The fauna of the Hawthorne formation 
has received but little attention and is practically unknown. The green 
clay and sands are reported to contain many oyster shells which are 
thoroughly silicified, and the phosphatic limestones and the chert beds 
are characterized by numerous specimens of an echinoid belonging to 
the genus Cassidulus. Molluscan remains are associated with this 
echinoid, but they have not yet been investigated. 
Structure:—The Hawthorne formation has been affected by broad 
earth movements similar to those which produced the peninsula of 
Florida. There is a gentle seaward dip which is seldom noticeable in 
single exposures, but may be determined by means of well records 
which show that the formation sinks below sea level on the east coast. 
There are probably dips both northward and southward from the 
central part of the peninsula, but the determination of their amount 
requires detailed study. The general easterly dips are known to be 
irregular in amount, but probably do not average more than 75-100 
feet to the mile. 
Local Details: — While the Hawthorne formation is well known, 
information concerning the detailed sections is comparatively meager. 
The most complete sections which have been recognized as belonging 
to this formation are those described by Dali . 3 At the type locality 
near Hawthorne the rock is phosphatic and has been mined and 
crushed for use as a fertilizer and at many other places the formation 
contains more or less phosphate. One of these localities is at the 
Devil’s Mill Hopper northwest of Gainesville, where the rock is ex- 
1 Dali, William H., Neocene of North America; U. S. Geol. Surv. Bull. 84, 
1892, p. 109. 
2 Ibid. p. 158. 
3 Dali, Wm. H., Neocene of North America, U. S. Geol. Survey Bull. 84, 
1892, pp. 107-112. 
