ON THE GOTHAM MARBLE 
145 
the intervals between deposition. Branching of the 
“ hedge ” is similarly produced. 
III. Detailed Account of the Origin of Gotham Marble. 
During hot, calm summer weather, the waters of a very 
shallow but extensive lagoon, only a few inches deep in . 
places, were so heated that by loss of carbon dioxide, and 
evaporation, carbonate of lime was precipitated, and 
shortly set into a firm layer at the bottom. Band after band 
followed, and thus the whole of the basement beds were 
laid down. In some places, spherical concretions were laid 
down instead, owing probably to the existence of some 
calcite nucleus of detrital origin. 
Then came autumn and winter, and with them — (a) less 
sun heat, (5) more rain, i.e., less deposition of the calcite, 
and (c) more silt. 
[I use the names of the seasons for simplicity’s sake. 
“ Summer ” means a period, of uncertain length, of dry 
years ; “ winter ” a corresponding period of wet years.] 
As a consequence precipitation stopped, and a somewhat 
impure calcareous silt, with occasionally a few shells, was 
washed over the basement beds to a depth of several inches. 
In the deeper parts, in which alone the Landscape Marble 
was deposited, there were no detrital shells, the water being 
too still to move them. 
When “ spring ” returned, chemical precipitation was 
gradually re-established. At first the supply was only 
sufficient to furnish a “ hedge.” Just at this time, the silt 
was nearly or quite exposed to the air for a short time, and 
therefore developed a tendency to crack into squares and 
polygons. That actually visible cracks appeared was only 
occasionally the case. And as the upper layers of the silt 
dried most, they tended to crack most. 
Now as precipitation recommenced, it not only deposited 
a “ hedge ” on the basement beds, but it also foj'med 
vertical walls in the silt enclosing polygons along these 
