2 BULLETIN 90, UNITED STATES NATIONAL MUSEUM. 



from which they came were known to collectors and later to visit- 

 ing geologists as " the Silex Beds," a place-name they have retained 

 to the present time. 



The process of silicification is still going on. When the writer 

 visited the locality in 1886 and on various subsequent occasions, 

 hoping that the limestone matrix might be removed by acid, a test 

 was made which showed that in cases where part of a fossil shell 

 projecting from a limestone pebble between tides, where the water 

 was gradually dissolving the limestone and exposing the fossil, the 

 still-imbedded portion of the shell retained its limy character, while 

 the exposed portion had been completely replaced by silex. 



The interest which these fossils possess is not limited to their 

 aesthetic beauty, nor their position as characteristic of one horizon 

 in the series illustrating the evolution of life on the globe, but is 

 of extreme importance as furnishing a key to the little-understood 

 succession of the Tertiary beds which fringe the islands of the West 

 Indies and the encircling continental shores of Mexico, Central 

 America, and northern South America. The Tertiary column of 

 the coastal i^lain of our Gulf States being fairly well elucidated, 

 the relative position of the deposits to the south can be determined, 

 if any one of them can be satisfactorily connected with a given hori- 

 zon in the North American series. Such a connection is afforded by 

 the fauna of the silex beds of Tampa. 



GEOLOGICAL EXPLORATION OF THE BEDS. 



The first account of these beds in geological literature was printed 

 in the American Journal of Science in 1846 ^ by Prof. John H. Allen. 

 His account is accurate and graphic, representing the characteristic 

 features of the deposit and its fossils as well as could be done to-day, 

 though without any attempt to determine their place in the geologi- 

 cal column. He states that even at that time the chalcedonized fos- 

 sils were well known to mineralogists. Later in the same year T. A. 

 Conrad published an account of his researches into Floridian geol- 

 ogy ^ made during a visit in 1842. He described the bed and the 

 fossils at length and refers them to the upper part of the Eocene. He 

 traced the formation correctly to the falls of the Hillsborough Kiver, 9 

 miles above Tampa, and again recognizes it "a few miles up the 

 Manatee Eiver in the bed of a rivulet." He points out that at Bal- 

 last point, near Fort Brooke, the beds containing silicified material 

 underlie a stratum of limestone which in turn is covered by a thin 

 layer of Pleistocene marl and shells. In the second part of his paper 

 he describes and figures nine species of invertebrates, including a 

 Balanus and two species of Foraminifera from these beds. 



1 Amer. .Journ. Sci., ser. 2, vol. 1, pp. 38-42, Jan., 1846. 



2 Idem., ser. 2, vol. 2, pp. 41-48, 399-400, July and Nov., 1846. 



