264 Davies — P/iosphatic Deposits in Nassau. 



very apparent, and present indications of having originated, first, 

 with dislocations of the strata before the phosphate of lime was 

 deposited (Fig. 2), and, secondly, with long continued aqueous and 

 atmospheric agencies ; the first by means of currents scooping out 

 grooves and miniature valleys, or by chemical action where the 

 water lay still, wearing hollows in the limestone, and the latter 

 slowly rounding the exposed edges of the beds (Fig. 3). 



The deposit occurs in the form of concretions, imbedded in a 

 matrix of clay ; these concretions are most irregular in their shape, 

 and vary in dimensions from the size of an apple to masses weigh- 

 ing two or three tons. It would also beem as if the original 

 concretions had, subsequently to their formation, been subjected to a 

 good deal of attrition : this is indicated by the preponderance of 

 small fragments, decreasing in size down to that of grains of sand. 

 Where the deposit assumes this form it is known locally as 

 Washstein. 



Besides this deposit of phosphate of lime resting upon the older 

 rocks there are also deposits of Hematite and Manganese, which 

 occur in just the same position, filling up the inequalities of the 

 limestone. As far, however, as my observation went, these deposits 

 are found in bulk around the outer margin of the phosphatic area. 

 Smaller portions of these, however, either held in solution by the 

 water in which all were deposited, or redistributed by currents, 

 have become mixed up with the j)hospliorite (Fig. 3), and have also, 

 in places, so permeated the latter as to reduce its per centage of 

 phosphate of lime so low that its commercial value is considerably 

 lessened. The Manganese and Hematite are also found in separate 

 deposits within the phosphatic area. 



Along the northern boundary, where the deposits border on the 

 development of the older rocks, we find the greatest admixture of 

 these extraneous matters, and the per centage of phosphate of lime 

 ranging below sixty per cent. ; but southward, towards Limburg, 

 the deposit improves in quality, containing, in places, as much as 

 ninety-two per cent, of phosphate of lime, and assuming the crystal- 

 line form of Apatite. 



As might be expected from the mode of its occurrence, the 

 deposit is most irregular in thickness, varying, even in the same 

 mine, from six inches to as many feet. It appears to attain its 

 greatest continuous thickness on a line ranging north-east and 

 south-west, and thins out gradually to the north-west and south- 

 east. To the north-west and west, the brown clay also becomes 

 thinner, and is found covered with splintery gi'avel (Quartzgeschiebe), 

 the detritus of neighbouring rocks. Hitlierto the discoveries of 

 phosphorite have been made only where limestone is the underlying 

 rock. With the limestone, generallj^ speaking, it appears to be co- 

 extensive, its presence or absence, however, in particular places, 

 will depend upon the presence or absence of deposits of iron ore or 

 Manganese, as well as the possibility of its having suffered denu- 

 dation in exposed places since its deposition. 



To the enquiry, whence came such an amount of phosphatic 



