12 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 73 



progenitors of these forms from Long Pine Key and landed them 

 here. 



It is probable that at the time of the first elevation the reef of 

 which the Upper Keys was formed was considerably developed and 

 raised to the surface of the sea or even somewhat above it in places, 

 but I doubt if it was clothed with hammock forest or inhabited by 

 land snails. The flora is composed of tropical plants and has been 

 almost wholly derived from Cuba, but it is comparatively poor, hav- 

 ing scarcely half as many such species as the Lower Keys and noth- 

 ing like as many as the southeast mainland, and this fact would 

 prove that it is much younger than either of the last-mentioned areas. 



Then there was a second period of subsidence during which the 

 land went down until the sea washed into the present bluffs at Coco- 

 nut Grove and Miami, eroding them in places into fantastic forms. 

 At Little River the depression amounted to some 7 feet, while at Big 

 Pine Key it was about 3 feet. 



An elevation followed during which the land was raised perhaps 

 to a few feet higher than it is at present. The Upper Keys were 

 elevated until they probably formed an unbroken chain or single 

 island. The sea attacked the reef, tearing it to pieces, scattering the 

 fragments and grinding them into sand, then cementing the wreck 

 firmly together and building it up into a solid, continuous island. 

 This great barrier for a long time prevented floating material from 

 landing on the mainland back of it, but it became more or less 

 covered with hammock forest and provided a home for such Liguus 

 as drifted in from Cuba. Several forms, either roseatus, castaneo- 

 zonatus^ vacaensis, Uneolatus, and perhaps mariiioratus or their 

 immediate progenitors, drifted in from Cuba and became established 

 long enough ago that they spread practically throughout the entire 

 length of the long, curving island. This was the heyday of the 

 Upper Keys, the period of their greatest development and glory. 

 A broad, irregular land bridge reached from the region of the Mate- 

 cumbes across to the mainland from Joe Kemps Key for 12 or 15 

 miles to the eastward. Li places this was swamp or shallow lagoon, 

 but there was continuous hammock-covered land, and over this 

 migrated a considerable variety of tropical vegetation from the keys; 

 in fact most of the flora of the south and southwest coasts of the 

 mahiland was derived from the Upper Keys in this way. This 

 flora differs considerably from that of the rocky ridge along the 

 southeastern mainland. It is nearly all tropical, while that of the 

 ridge is mixed — West Indian and warm temperate — the latter part 

 being derived from the northward. The reason for this is that the 

 Everglades stretches, and since the first elevation has stretched, in 

 a broad, unbroken area from near Whitewater Bay eastward and 

 northeastward to Cutler, forming an effectual barrier against the 



