116 Papers from the Marine Biological Laboratory at Tortugas. 



fragments and amorphous carbonate of lime. The special point in call- 

 ing attention to the specimens from the southern end of the cape on the 

 east side of Biscayne Bay and from the two succeeding keys to the 

 south, Virginia Key and Key Biscayne, is to emphasize the presence on 

 them of a large proportion of quartz sand. Cape Florida, which is the 

 southern extremity of Key Biscayne, has its surface covered by siliceous 

 sand with an admixture of comminuted shells. 



Soldier Key, the next key to the south of Cape Florida, has on its 

 summit and western side a coating of siliceous sand underlain by elevated 

 coral reef rock. Proceeding southward along the main line of keys the 

 siliceous constituents progressively diminish. 



Attempts were made to obtain bottom samples at two places on the 

 east side of Key Biscayne, but in both instances the bottom was hard and 

 no specimens were procured. 



Three bottom samples were obtained from the northern end of 

 Biscayne Bav, Nos. i, 3, and 5. Specimen No. i, which was collected 

 a short distance off the mouth of the Miami River, showed shell frag- 

 ments, amorphous carbonate of lime, much quartz sand, sponge spicules, 

 and diatoms. The presence of quartz sand is to be expected, as it forms 

 the surface coating over the Miami oolite of the surrounding country. 

 Specimen No. 3, which was taken between the mouth of the Miami River 

 and the western point of Key Biscayne in about 12 feet of water, was 

 composed mostly of shell fragments and amorphous carbonate of lime, 

 with very little quartz. Specimen No. 5, which was taken in about 13 

 feet of water off West Point, Key Biscayne, was also composed of shell 

 fragments, amorphous carbonate of lime, and considerable quartz, with 

 some sponge spicules and diatoms. 



One specimen, No. 12, collected from the northeast corner of Key 

 Biscayne, depth 2.5 feet, contained shell fragments, calcite, amorphous 

 carbonate of lime, and considerable fine quartz, the quartz passing 

 through the 40 and 80 to the inch mesh sieves, showing some silica on 

 the sea floor east of this key. The bottom off the southwest corner of 

 Key Biscayne consists of calcareous ooze and comminuted shells. 



Five specimens, Nos. 13 to 17, were obtained from the southern end 

 of Biscayne Bay, from the latitude of Sands Key southward. An inspec- 

 tion of Mr. Matson's table will show that most of the material is fine; 

 by far the larger portion passed through the 40-mesh sieve but was 

 retained by the 80. Quartz is abundant in No. 13, and there is some in 

 Nos. 14, 15, and 16. In No. 16, however, the siliceous component is 

 comparatively small in amount, while in No. 17 fine quartz, all of which 

 passes through No. 80 sieve, is rare. 



These observations on the bottom deposits of Biscayne Bay indicate 

 that considerable quartz is being washed into the northern end of the 

 bay, and that as one proceeds southward the calcareous constituents 

 become predominant, while the siliceous constituents become insignifi- 

 cant. The material, when collected, consisted mostly of oozes and no 

 intimation of the formation of oolite was observed. 



