.4 Contribution to the Geologic History of the Floridian Plateau. 117 



BETWEEN OLD RHODES BANK AND CARYSFORT REEF LIGHT. 



Two specimens, Nos. 18 and 19, were collected between Old Rhodes 

 Bank and Carysfort Reef Light. Both of these specimens consisted 

 mostly of shell fragments, amorphous carbonate of lime, sponge spicules, 

 diatoms, and a very little quartz. In this region quartz is rare outside 

 the main line of keys. 



CARD SOUND. 



Three specimens were collected from this sound, Nos. 20, 21, and 

 22, and one, No. 23, was taken from Steamboat Creek between Card and 

 Barnes sounds. Nos. 20 and 21 both contained considerable quantities 

 of quartz as well as shells, shell fragments, amorphous carbonate of lime, 

 sponge spicules, and diatoms. In No. 22, however, quartz was rare. 

 Specimen No. 23 from Steamboat Creek consisted mostly of organic 

 matter with some amorphous carbonate of lime, sponge spicules, diatoms, 

 and a very little quartz. 



BARNES SOUND. 



Only two specimens were taken from Barnes Sound, the first, No. 24, 

 near the mouth of Steamboat Creek, at a depth of about 12 feet; the 

 other, No. 25, near the center of the sound, depth about 11 feet. Speci- 

 men No. 24 in Mr. Matson's table is queried and perhaps should be 

 omitted from the discussion. No. 25 consists mostly of shells, shell 

 fragments, amorphous carbonate of lime, sponge spicules, and diatoms, 

 with very little quartz, indicating a progressive diminution of quartz 

 toward the southwest. 



BLACKWATER SOUND. 



Two samples, Nos. 26 and 27, were obtained from this sound. No. 

 27, it appears, was lost. No. 26, which was taken from the upper end of 

 the sound off the mouth of Jewfish Creek, depth 12 feet, consisted 

 of organic matter, shells, shell fragments, calcite and aragonite, sponge 

 spicules, and a little quartz was retained by sieves Nos. 40 and 80. 

 Material thrown out of a canal dredged between Blackwater and Hoodoo 

 sounds was similar to that forming the bottom of the neighboring sounds, 

 except molluscan remains are so abundant as to constitute a shell marl. 



HOODOO SOUND. 



This is a small sound between the lower end of Blackwater Sound 

 and Florida Bay. One specimen, No. 28, was obtained from it at a 

 depth of about 6 feet. The material was similar to that from Black- 

 water Sound with somewhat less quartz. 



FLORIDA BAY. 



Specimens Nos. 29 to 47 were taken from Florida Bay. Nos. 39 to 

 42, and No. 47, were procured on the north side of the k'evs elongated 

 in a northeast-southwest direction. Nos. 43 to 46 were collected along 

 the group of keys lying slightly to the west of Bahia Honda and 

 elongated in a northwest-southeast direction. 



North Side of Key Largo. — Nos. 29, 30, and 32 were obtained north 

 of Key Largo in depths ranging from 1 foot to 7 feet; No. 31 is from 



