118 Papers from the Marine Biological Laboratory at Tortugas. 



the surface of Pigeon Key. The material in general was similar in com- 

 position, except the quantity of shells and shell fragments varied. Only 

 one sample, No. 31, which is the surface material of Pigeon Key, 1 con- 

 tained any quartz. No. 32 was taken off the inner end of Tavernier 

 Creek, which forms the lower limit of Key Largo. 



North of Long Island. — One sample, No. 33, was collected on the 

 shoals northwest of Tavernier Creek, about a mile off Long Island. 

 The material consisted of shells, amorphous carbonate of lime, sponge 

 spicules, and diatoms; no quartz was noticed. 



North of Upper Matecumbe. — Between McGinty and Torrey keys one 

 specimen, No. 34, was obtained. It consisted of shell fragments, amor- 

 phous carbonate of lime, sponge spicules, diatoms, and some calcite, 

 and in the material retained by sieves Nos. 80 and 100 considerable 

 quartz was observed in the 22.9 per cent of the total weight of the sample 

 examined. This sample shows that quartz has worked its way as far to 

 the southwest as a point nearly opposite the lower end of Upper Mate- 

 cumbe Key. The bottom of the channel southwest of Shell Key is swept 

 clean by the currents passing between Upper and Lower Matecumbe keys. 



North of Lower Matecumbe. — Two samples, Nos. 35 and 36, were 

 obtained on the north side of this key: No. 35, a mile northwest of Shell 

 Key; No. 36, the southwestern end of the cut across the banks south of 

 Bowlegs Key. Both specimens consisted mostly of shell fragments, 

 amorphous carbonate of lime, sponge spicules, and diatoms, with very 

 little quartz. 



North of Long Key. — A specimen, No. 37, obtained from 2.25 miles 

 northwest of the upper end of Long Key, consisted mostly of calcareous 

 material with sponge spicules and diatoms. There was very little quartz 

 and a few calcareous oval grains. There is some doubt about the identi- 

 fication of the specimens from localities 38 and 39 and they are omitted 

 from the discussion. However, the bottom a mile west of north of the 

 western end of Long Key is hard, being swept almost clean by currents 

 passing between Long and Grassy keys. The bottom material north of 

 Grassy Key is a calcareous ooze with a little quartz (field examination). 



North of Key Vaca. — Specimens Nos. 40, 41, and 42 were collected 

 along the north side of this key. The material .consisted of shell frag- 

 ments, amorphous carbonate of lime, sponge spicules, and diatoms. 

 There were a few oval grains in specimen No. 40 and a very little quartz 

 in each of the three. The bottom between Key Vaca and Bahia Honda, 

 midway between Molasses and Duck keys, depth 9 feet, is hard and 

 covered by a thin coating of shells and shell fragments. 



North of Bahia Honda. — Specimen No. 47 was obtained 0.75 mile 

 north of this key in a depth of 12 feet It consisted of shell fragments, 

 amorphous carbonate of lime, sponge spicules, diatoms, and a very little 

 quartz. Bahia Honda is the westernmost of the main line of keys with 

 a northeast-southwest trend. 



No Name and Big Pine Keys. — Four specimens, Nos. 43, 44, 45, and 

 46, obtained in this vicinity, consist mostly of calcareous material with 

 some sponge spicules and diatoms. Oval grains were in three specimens, 



1 This is important in indicating the southward extent of surficial quartz. 



