14 DEPOSITS OF PHOSPHATE OF LIME. [bull. 46. 
States. At present it can only be said that they afford the conditions 
which, so far as the theory goes, should lead to the accumulation of 
phosphatic deposits of greater or less importance. It will be a simple 
matter to explain these deposits, though it is a task requiring a pa- 
tient study of a large field. Although it is likely that the phosphatic 
materials will be found aggregated into nodules at many points in this 
area it will not be safe to assume that they will be found in the same 
form as those which occur about Charleston, S. C. The nodules found 
in the beds about the last named point, though in my opinion originating 
beneath swampy deposits, have apparently been, in part at least, swept 
from their original beds by the rivers which enter the sea at that point 
and have thus been concentrated in estuarine deposits. 
Although local concentrations of phosphatic nodules other than those 
now known may well be sought for in the Southern States, I do not 
think that the precise conditions or character of the deposits as found 
at Charleston should be expected to repeat themselves elsewhere. It 
is characteristic of the process of concentration of phosphatic, as well 
as of other matter into nodules that the material takes on a great 
variety of aspects, each proper to a particular site, and this although 
the surrounding circumstances of the several localities may apparently 
be identical. 
Next lower on the geologic section we have, in the Tertiary region of 
the Mauvaises Terres, extensive deposits of vertebrate remains which 
may possibly yield some commercially important supplies of bone phos- 
phates. Although none of the existing sources of supply of these ma- 
terials come from deposits of the nature of those found in Nebraska, 
the conditions of that remarkable region are so peculiar that it will not 
be well to pass it by without inquiry. 
While the American Cretaceous deposits are, as a whole, decidedly 
different from those of the Old World, the Greensand beds of the 
section in the two countries present considerable likeness in their char- 
acters. It is probable that in this country, as in Europe, considerable 
parts of the Cretaceous section are somewhat phosphatic, and that those 
beds containing disseminated phosphatic matter have been in many 
places exposed to the process of leaching in former geologic periods. 
Therefore we may reasonably search in the Cretaceous beds of this 
country for the same class of phosphatic deposits which have proved so 
important in the northern parts of Europe. 
Although some peculiar deposits of phosphate have been found in the 
Devonian rocks of Nassau, it may safely be assumed that below the line 
of the Cretaceous we have no facts to guide us in our search for phos- 
phates until we come to the horizon of the Upper Silurian limestones, at 
about the level of the uppermost beds of the Upper Silurian, as far as 
that level can be determined by the perplexing assemblage of fossils. 
There occurs in Bath County, Ky., a thick bed of much decayed, very 
phosphatic siderite. This deposit covers but a small area and con- 
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