CONDITIONS OF SEDIMENTARY DEPOSITION. 5 I 3 



were filled with hard, coarsely crystalline limestone. The rock 

 was not coquina modified, but looked more like a fossilized oyster 

 reef. It contained no corals, and was obviously Pleistocene. 

 The rock formed the base of small islets of drier soil amid the 

 marsh, on which islets grew pine trees. The marsh, apart from 

 these islets, is probably entirely submerged in the rainy season." 



In the bulletin referred to Dall speaks of the rock obtained 

 by Willcox as being of organic or of partly organic and partly 

 chemical origin, but at the time that manuscript was prepared 

 the observations were less complete than now. In a recent let- 

 ter he says: " Mr. Willcox's observations on the deposition of 

 the flocculent mud from lime -bearing water were later than the 

 original statement. The precipitated mud is more or less me- 

 chanically mixed with masses of the corrallia of Polyzoa and 

 bivalve shells driven in shore by the sea, but these creatures do 

 not live in the muddy water, but in the clearer water outside." 



Through the courtesy of Dr. Dall the writer has examined 

 specimens of this rock. It is a light cream-colored mass of 

 crystalline calcite formed around the included fragments of 

 shells. Under the microscope the unaltered structure of the 

 organic fragments is strikingly different from that of the coarse 

 holocrystalline matrix, in which it is apparent that the crystals 

 developed in place. Were this a limestone of some past geo- 

 logic period it would be concluded, on the evidence of the crys- 

 talline texture of some parts of it, that it had been metamor- 

 phosed and that the organic remains now visible had escaped 

 the process which altered the matrix. But the observed condi- 

 tions of its formation preclude the hypothesis of secondary crys- 

 tallization. Apparently, the crystalline matrix is one primary 

 product from solution, a rock formed in contact with the 

 bottom, the calcareous mud is another, which, being precipitated 

 in the solution, remains an incoherent sediment. 



These results may perhaps be thus explained: The drain- 

 age of the peninsula contains an unusually large amount of lime, 

 in consequence of the abundant supply of carbonic acid and 

 other products of vegetable decay in the sub-tropical climate and 



