62 TRANSACTIONS OF THE WAGNER FREE 



bluish masses scattered over the latter, seemingly representing a newer 

 formation. It contains numerous fossil impressions, partially silicified, a 

 number of them, as the Venus pcnita above mentioned, identical with forms 

 found in the limestone, but the greater number distinct. Among these 

 the remains of one or more species of Cerithium are especially abundant, 

 and might be said to determine the faunal character of the rock. We 

 found no traces of the orbitolite. At 110 place could I detect a solid 

 outcrop of the rock, and, therefore, from the observations made at this 

 point alone it would be impossible to determine the stratigraphical 

 relations of the two series of deposits occurring here. But along the 

 Hillsboro River and on a small tributary, known as Magbey's Spring, 

 which enters a short distance above the town of Tampa, the relationship 

 is very clearly shown. The hard siliceous blue rock, charged with the 

 remains of Cerithium, etc., appears at scattered intervals all along the 

 river bank, now on one shore then on the other, and manifestly forming 

 the bed of the channel. Just below the shipyard the nearly horizontal 

 strata lie in beds of from one to two feet thickness. I was unable to 

 determine any true dip. The orbitolite limestone is exposed a short 

 piece above this point on Magbey's Spring, about three or four hundred 

 feet from the borders of the Hillsboro, in a heavy mass some seven to ten 

 feet in thickness. Although the irregularity of the outcrop and its small 

 extent prevented me from locating its absolute position, there can be 

 no question, seeing its proximity to, and elevation above the river, that 

 it overlies the blue rock of the channel. This must then also be the* 

 relation existing between the two kinds of deposits exhibited at Ballast 

 Point, which are manifestly the equivalents of the Hillsboro series. The 

 big irregular masses or boulders which here extend into the bay, or 

 lie scattered over the limestone, are evidently exposed as the result of 

 outwash, and appear to have been scattered to their present positions 

 through the action of a heavy sea. 



The relations of the coralliferous deposit exposed at Newman's landing, 

 as well as of the two other classes of rock just described, are fully set 

 forth on pp. 120-123, and require little further consideration. An enum- 

 eration of the species of fossils occurring here is given on pp. 1 19-120, 

 and 124. The fossils are nearly all completely silicified, and exhibit to the 

 minutest detail the ornamentation characteristic of the different species. 

 The coral geodes, some of them measuring as much as eight or ten 

 inches across, are especially beautiful, and exhibit to good advantage the 

 mammillated character of the substituting blue and blood chalcedony. 

 There is little doubt in my mind that the formation is due to an infil- 

 tration of silica in a heated condition, but in what precise manner the 

 peculiar method of hollowing was brought about I am unable even to 

 guess at. Many of the species so closely resemble recent forms that it 



