.4 Contribution to the Geologic History of the Floridian Plateau. 1 1 1 



Honda Key. Key Largo, the largest, has a maximum width of about 

 3.5 miles and is about 27 miles in length. 



(2) Beginning with Little Pine and No Name keys, the axis of elon- 

 gation is from northwest to southeast, or practically at right angles to 

 the first group. This group includes the keys between Bahia Honda and 

 Boca Grande, although one key, Key West, has its longer axis east and 

 west, and not north and south. The largest of these keys, Big Pine, has 

 the following dimensions: length 8 miles, width of southern end 2.375 

 miles, average width about 1.25 miles. 



(3) The third group comprises the rather typical atoll of the Mar- 

 quesas and the less perfect one of the Tortugas. 



In composition the keys represent four types: 



(1) The most northern group, comprising Virginia Key and Key 

 Biscayne, has its surface composed of sands, largely arenaceous (plate 6, 

 figs, a and b). 



(2) Those from Soldier Key to Bahia Honda inclusive and the 

 southern end of Big Pine are elevated coral reef rocks (plate 15, figs. 

 b and c). 



(3) The group from Little Pine and No Name to Boca Grande are 

 formed of oolite, the Key West oolite (plate 14, fig. c; 15, fig. a). 



(4) The Marquesas and the Tortugas show on their surfaces the 

 more or less comminuted remains of the calcareous skeletons of organ- 

 isms, mollusks, corals, nullipores, etc. (plate 6, fig. c; 7, figs, a and b, 

 and text figs. 1 and 2). 



THE BAYS AND SOUNDS BEHIND THE KEYS. 



The landward face of the keys is bounded by a series of bays and 

 sounds, beginning at the north with Key Biscayne, followed, going south- 

 ward, by Card, Barnes, Blackwater, and Hoodoo sounds, and terminated 

 westward by the Bay of Florida. 



Biscayne Bay has a more pointed northern end, bounded on the 

 eastward by a sandy spit of land, Virginia Key, and Key Biscayne, 

 between which are passages. Its southern portion is wider, bounded 

 on the east by Sands, Elliott, and Old Rhodes keys, and has an obtuse 

 termination before communicating with Card Sound, to the south. 

 The length of this bay is 35 miles, maximum width 10 miles, maxi- 

 mum depth 17 feet. Featherbed Bank extends across its median portion 

 and makes two divisions. 



Card Sound has its northern end almost opposite the northern end 

 of Key Largo, toward which point is a projection from the mainland; its 

 southern end is formed by a spur projecting from Key Largo toward 

 the mainland. The length of this sound is 6 miles, width 3 to 3.5 miles, 

 maximum depth 12.5 feet. 



Barnes Sound has as its northern boundary the spur from Key 

 Largo, forming the lower end of Card Sound; its southern boundary is 

 formed by projections from Key Largo and the mainland. Its length 

 is 6.5 miles, width 5.5 miles, maximum depth 11 feet. 



Blackwater Sound is south of Barnes Sound, and has its northern 

 boundarv determined by the features forming the southern boundary 



