(jeoloyic Time. — Waleotl. 355 
•'Theoretically either one of three things may occur to the neutra! 
carbonate of lime, if it be thrown out of solution by either one of these 
processes. The carbonate may be redissolved, deposited as a calcareous 
mud, or built into organic structures. ,- He studied some recent lime 
stone 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 frag 
ments 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 con 
eluded, 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 sec- 
ondary crystallization.''* Apparently the crystalline matrix is one 
primary product, and the calcareous mud is another, which being pre- 
cipitated in the solution remains an incoherent sediment. 
I think we may accept the conclusion that the deposition of carbon- 
ate of lime is by both organic agency and chemical precipitation. It 
is not necessary to speak of deposition by mechanical methods except 
in relation to the deposition of chemically derived granules. Thi» 
probably takes place, and may be a very important factor in the forma- 
tion of limestones, in seas receiving a large supply of calcium from 
the land. Calcareous conglomerates do not enter as a prominent de- 
posit in the Cordilleran area. 
There is no evidence in the marine geologic formations of this conti 
nent 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. Limestones 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 accumulated in deeper water. The conditions in the Cordilleran 
sea were, I think, more favorable for rapid deposition than in the deep 
open ocean, but probably not as favorable as about coral reefs and 
islands. The limestones and often the contained fossils clearly indicate 
the presence of many of the same conditions of deposition as described 
by the authors I have quoted. More or less decomposed shells occur in 
nearly every limestone: and a large proportion of limestones, especially 
the non-metamorphic marbles, clearly show that they were deposited 
under the influence of the agencies at work in the laboratory of the sea. 
Willis states that this occurs in the shallow waters of the Everglades of 
Florida, and there is no a priori reason why it did not occur throughout 
geologic time:— on the contrary, there is no doubt that it did. 
Rate of deposit in former times. It has frequently been assumed 
that in the earlier epochs the conditions were more favorable for rapid 
denudation and in consequence thereof the transportation and deposi- 
tion of sediment was greater. Prof. Prestwich considers -1 " that prior to 
~8ee Mr. Willis article in Jonrnal of Geology, Chicago, Joly-Aotfust. 
lotry, vol. r. 1S86, pp. 60-6L 
