shaler.] INTRODUCTION. 13 
many of the details of this process to adapt it to the peculiar circum- 
stances of particular deposits, it seems to me that it is the key to the 
most common forms of superficial accumulations of nodular phosphates. 
In an admirable description of the phosphate beds in the neighborhood 
of Mous, in Belgium, by Mr. F. L. Cornet, 1 that distinguished author 
has independently propounded this simple hypothesis, and several 
other writers on the subject have apprehended the importance of this 
leaching action. 
It is evidently essential to this process of concentration that the sur- 
face of the deposits which are leaching away should have been preserved 
from the action of mechanical erosion, which would have prevented the 
formation of phosphatic concentrates. 
Inquiry into the conditions of the swamp deposits of this country has 
satisfied me that beneath the surface of many of our fresh- water marshes, 
and probably in a lesser degree beneath the marine deposits of the same 
nature, there isa more or less important concentration of lime phosphates 
constantly going on. The effect of this action is seen in the remarkable 
fitness of these fresh- water swamp soils for the production of grain 
crops. For instance, in the case of the Dismal Swamp district in Vir. 
ginia and North Carolina we find that the soils on which the swamp de- 
posit rests are extremely barren, while in the mud that has accumulated 
beneath the swamp we have a rich store of phosphates, potash, and 
soda, which causes the soil of these swamps to be extremely well suited 
to grain tillage as soon as it is drained. In a similar way in the swamps 
of New England and elsewhere we find the bog-iron ores which are fre- 
quently accumulated in their bottoms very rich in phosphatic matter. 
The evidence is not yet complete that this phosphatic material becomes 
aggregated into nodules in the swamp muds, but the number of cases 
in which nodules have been found in this position makes it quite likely 
that the nodulation of the material may go on in that position. The 
present condition of the inquiry goes, in a word, to show that wherever 
we have a region long overlaid by swampy matter we may expect a 
certain concentration of lime phosphates in the lower part of the marsh 
deposit. Wherever the swamp area lies upon somewhat phosphatic 
marls which have been slowly washed away by the downward leaching 
of the waters charged with the acids arising from decayed vegetation, 
or where the swamp deposits, even when not resting on such marls, are 
in a position to receive the waste from beds containing phosphates, we 
may expect to find a considerable concentration of phosphatic matter 
in the swamp bed. By the erosion of these swamps we may have the 
nodules of phosphate concentrated in beds such as occupy the estuaries 
of the rivers near Charleston, S. C. 
The area of swamp lands which fulfill these conditions is very large. 
They exist in numerous areas in more than half the so-called Southern 
1 See Quart. Jour. Geol. Soc. Loudou, vol. 42, 1886, p. 325. 
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