GEOLOGICAL HISTOKY OF FLOKIDA 171 



the end of the Miocene Period, while a slight depression 

 occurred in Pliocene times, and little change since. Whether 

 the tropical flora of southern Florida, or part of it at any rate, 

 is the relict of an Oligocene invasion from the south is left 

 undetermined by Dr. Dall's researches. Yet, from the fact 

 that a species of the terrestrial mollusk Glandina occurs in 

 the Pliocene Caloosahatchie beds of south-western Florida, 

 we might be led to infer that other southern forms might 

 have survived on the peninsula till Pliocene and possibly 

 recent times. 



Dr. Hill concurs in so far with Dr. Dall's conclusions 

 as he establishes in Jamaica signs of a tremendous orogenic 

 movement in late Oligocene or Miocene times, resulting in an 

 uplift whereby many of the West Indian Islands and pos- 

 sibly an insular southern portion of Florida became united 

 with one another. In Miocene or early Pliocene the islands, 

 according to Dr. Hill,* were severed from one another by 

 submergence, assuming gradually their present outlines which 

 they have since retained. 



That some kind -of union of the island of Florida with the 

 West Indies took place in Miocene times is likewise indicated 

 by Dr. Matthew f in his attempt to delineate the hypothetical 

 outlines of the continents in Tertiary times, for he distinctly 

 unites southern Florida and Cuba by land. 



According to Dr. Vaughan,J the Florida plateau already 

 existed in pre -Oligocene times, but it was only towards the 

 end of the Oligocene Period that a portion of the plateau rose 

 above the sea and apparently remained so ever since. 

 Although this constituted 'Only a small island (" Orange 

 island " as he calls it), the deposits of the whole plateau are 

 full of sand and arenaceous material implying proximity of 

 land. 



From the opinions cited on the geological history of Florida 

 it is evident that there is nothing distinctly antagonistic to 

 the view that part of the tropical flora of southern Florida 

 is a relict from Tertiary times, many of the pecies being 



* Hill, Eobert T., "Geology of Jamaica," p. 224. 



t Matthew, W. D., " Continents in Tertiary Times," p. 366. 



t Vaughan, T. W., " Geologic History of Floridian Plateau." 



