GEOLOGIC TIME. 657 



" Theoretically either one of three things may occur to the 

 neutral carbonate of lime, if it be thrown out of solution by 

 either one of these processes. The carbonate may be redis- 

 solved, deposited as a calcareous mud, or built -into organic 

 structure." He studied some recent limestone deposited in the 

 Everglades of southern Florida and found it to be formed of 

 fragments of shells embedded in calcite. He states that, " 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 geologic period it 

 would be concluded, on the evidence of the crystalline texture 

 of some parts of it, that it had been metamorphosed, and that the 

 organic remains now visible had escaped the process which 

 altered the matrix. But the observed conditions of its formation 

 preclude the hypothesis of secondary crystallization." 1 Appar- 

 ently the crystalline matrix is one primary product, and the cal- 

 careous mud is another, which being precipitated in the solution 

 remains an incoherent sediment. 



I think we may accept the conclusion that the deposition of 

 carbonate of lime is by both organic agency and chemical pre- 

 cipitation. It is not necessary to speak of deposition by mechan- 

 ical methods except in relation to the deposition of chemically 

 derived granules. This probably takes place, and may be a very 

 important factor in the formation of limestones in seas receiving 

 a large supply of calcium from the land. Calcareous conglom- 

 erates do not enter as a prominent deposit in the Cordilleran area. 



There is no evidence in the marine, geologic formations of 

 this continent that they were deposited in the deep sea ; on the 

 contrary they are unlike such deposits and bear positive evidence 

 of having been laid down in relatively shallow waters. Lime- 

 stones with ripple-marks and sun cracks occur, and beds of 

 ripple-marked sandstones alternate with shales and limestones. 

 The more massive limestones, however, appear to have accumu- 

 lated in deeper water. The conditions in the Cordilleran sea 

 1 See Mr. Willis' article in Journal of Geology, Chicago, September, 1893. 



