146 



SCIENCE. 



[Vol. XIII. No. 316 



lar 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 Mons, in Belgium, by Mr. F. L. Cornet,' that distinguished au- 

 thor has independently propounded this simple hypothesis, and 

 several other writers on the subject have apprehended the impor- 

 tance of this leaching action. 



It is evidently essential to this process of concentration that the 

 surface of the deposits which are leaching away should have been 

 preserved from the action of mechanical erosion, v^hich 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 is a 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 Virginia and North Carolina, we find 

 that the soils on which the swamp deposit rests are extremely bar- 

 ren, 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-till- 

 age 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 

 frequently 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 over- 

 laid by swampy matter we may expect a certain concentration of 

 lime phosphates in the lower part of the marsh deposit. Wher- 

 ever 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 phos- 

 phates, 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 fulfil these conditions is very 

 large. They exist in numerous areas in more than half the so- 

 called Southern 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 im- 

 portance. It will be a simple matter to explain these deposits, 

 though It is a task requiring a patient study of a large field. Al- 

 though it is likely that the phosphatic materials will be found ag- 

 gregated 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 phosphates. Although none of the existing sources of supply 



^ See Quarterly Journal of the Geological Society, London, xlii., 1886, p. 325, 



of these materials come from deposits of the nature of those found 

 in Nebraska, the conditions of that remarkable region are so pecul- 

 iar that it will not be well to pass it by without inquiry. 



While the American cretaceous deposits are, as a whole, de- 

 cidedly different from those of the Old World, the greensand beds 

 of the section in the two countries present considerable likeness in 

 their characters. It is probable that in this country, as in Europe, 

 considerable parts of the cretaceous section are somewhat phos- 

 phatic, and that these beds containing disseminated phosphatic 

 matter have been in many places exposed to the process of leach- 

 ing in former geologic periods : therefore we may reasonably search 

 in the cretaceous beds of this country for the same class of phos- 

 phatic 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 phosphates 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 per- 

 plexing 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 consists of a patch of limestone of 

 about fifteen feet thick, which has been converted into siderite by 

 the inleaching of iron-bearing waters from the ferruginous Ohio 

 (Devonian) shales which formerly overlaid the bed. Since the 

 escarpment of the Ohio shales retreated beyond this bed, it has been 

 subjected to oxidation, and is now in the main converted into a 

 much-decayed limonite. Beneath this limonite there is a greenish 

 argillaceous sand, which contains frequent nodules of lime phos- 

 phate. These nodules are smooth-surfaced, and not unlike some 

 of the nodules from the Carolina district. They contain as much 

 as 92 per cent of lime phosphate. It seems likely that these nod- 

 ules were formed by the leaching-out of the lime phosphate from 

 the overlying ferruginous layers, which has completely removed the 

 lime carbonate, but has not removed the whole of the less soluble 

 lime phosphate. 



SECTION AT I 



COUNTY, KY. tPRESTON 



Although this deposit of nodules is not of sufficient abundance to 

 have any economic value, it is clear that we have in it an indication 

 of a method where, by a slight variation of the conditions, impor- 

 tant beds of nodular phosphates might be found. 



In the horizons of the Cambro-Silurian section, or, as it is gen- 

 erally called, the lower Silurian, there is much greater reason to ex- 

 pect the occurrence of workable phosphates than in the beds imme- 

 diately above. It is likely that the most important of the Spanish 

 deposits belong in strata of this period, and the Welsh deposits of 

 this general age are of noteworthy extent. We know, moreover, 

 that the commoner marine animals of this part of the geological 

 section were particularly adapted for the secretion of lime phos- 

 phate. 



The search of this portion of the section for phosphates should be 

 directed to two ends : first, to finding beds of very phosphatic lime- 

 stone; and, second, to discovering veins formed by a segregation 

 of lime phosphates either in the form of the Spanish deposits referred 

 to by Dr. Penrose or in the condition of nodular accumulations. 

 The area of rocks of these lower Silurian and Cambrian periods in 

 this country is very extensive, and so far there has been no search of 

 them for phosphatic materials. The little work done in Kentucky 

 during the above-mentioned geological survey served only to shov/ 

 that the proportion of lime phosphate in the rocks is extremely 

 variable, and that in certain beds it is so considerable that the ma- 



