20 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 73 



cut up into islets. One form of crenatus landed at Lauderdale and 

 spread southward; several came to the great Miami forest and, as 

 the land was raised and developed, hammocks spread southward and 

 southwestward along the low, rocky ridge. It is doubtful whether 

 the reef became high enough for hammock and snails to develop on 

 it at this time, but the sea no doubt attacked and spread it. 



During a subsidence following, the coral reef probably grew up as 

 fast as the land went down. The water of the Gulf of Mexico driven 

 by furious northers began to erode the north shore of the great island 

 and was driven in places entirely through it, finally cutting up a 

 considerable part of it into islands running exactly in the direction 

 of the wind. Sea water entered what was probably solider rock 

 at the west end and ate it into a complicated archipelago. LigvMS 

 solidus pictus, found only on Big Pine Key, is perhaps a recent ar- 

 rivel coming long after the great island was dismembered. 



When the land was elevated again it reached a higher level than 

 now, and as it rose the sea kept tearing at the reef and consolidating 

 it until at the time of highest land it was no doubt a single long 

 curving island with continuous hammock and a number of Liguus 

 which came from Cuba were thrown on it and had time to spread 

 throughout its length. At this time there was a broad land bridge 

 across from the Matacumbes to the south mainland. The flora of 

 the Upper Keys is tropical but meager in species, and this would 

 prove that the chain was much younger than the southeast mainland 

 or the Lower Keys, which have a far richer tropical flora. 



Many species of these West Indian plants crossea on the con- 

 tinuous hammock of the old bridge and now constitute almost the 

 entire flora of the south shore and southwest coast. Through this 

 hammock Liguus marvioratus^ vacaensis, roseatus, lineoJatus, ca^- 

 taneozonatus, and no doubt OxystyJa -fio^ndensis crossed to the main- 

 land and became established there, perhaps during the time when 

 there was the highest land elevation. Matecmnbiensis landed on the 

 key it was named for after the dismemberment of the Upper Keys 

 but before the destruction of the bridge, and crossed. Dry-land 

 connection between the south shore and the rocky ridge was pre- 

 vented by the Everglades which stretched from Cutler to White- 

 water Bay and had done so from the first. Several forms belonging 

 to the Upper Keys were carried to the southeastern mainland across 

 the bays by hurricane agency. The Cape Sable region is very 

 recent, the capes being sand washed up on an old mangrove swamp. 

 The sea is thrown in upon that region by hurricanes with terrific 

 force, and as the water is driven into Florida Bay and is prevented 

 from flowing south by the keys it overflows the Sable and southern 

 shore regions and Liguus and Oxystyles are distributed hit and miss. 



