Editing Biscayne National Park (section)

===Geology===
[[File:Biscayne underwater NPS1.jpg|thumb|alt=Sunlight on an underwater coral reef|Underwater view of a [[coral reef]] at Biscayne National Park]]
[[Biscayne Bay]] marks the southernmost extent of the Atlantic barrier islands, represented by [[Key Biscayne, Florida|Key Biscayne]] and the northernmost extent of the [[Florida Keys]] at [[Elliott Key]]. The keys are distinguished from the barrier islands by the coral limestone that extends to the islands' surface under a thin veneer of topsoil, while the barrier islands are dominated by wave-deposited sands that cover most of the limestones.<ref name=bryan1>Bryan ''et al.'', p. 288</ref> Biscayne Bay lies between low ridges of [[Oolite|oolitic]] Miami Limestone on the west, forming [[Cutler Bay, Florida|Cutler Ridge]] and the coral-based Key Largo limestone that underlies Elliott Key and the keys to the south. The Miami limestone was deposited in turbulent lagoon waters.

The Key Largo Limestone is a fossilized coral reef formed during the [[Sangamonian]] Stage of about 75,000 to 125,000&nbsp;years ago. The Miami Formation achieved its present form somewhat later, during a glacial period in which fresh water consolidated and cemented the lagoon deposits.<ref>Bryan ''et al.'', pp. 287–290</ref> The Key Largo Limestone is a coarse stone formed from stony corals, between {{convert|69|and|200|ft|abbr=on}} in thickness.<ref>Bryan ''et al.'', p. 298</ref> As a consequence of their origins as reefs, the beaches of Elliott Key and Old Rhodes Key are rocky. Significant sandy beaches are found only at Sands Key.<ref name=bnmecology>{{cite web|title=The Ecology|work=Biscayne National Monument: A Proposal|url=http://www.nps.gov/parkhistory/online_books/bisc/proposal/sec4.htm|publisher=National Park Service|access-date=7 January 2013}}</ref>