February 



22, i< 



•] 



SCIENCE. 



145 



phosphatic manures. The importance of such manures has so far 

 been well recognized only by the cotton-growers of this country, 

 yet it is evident that in a short time this class of fertilizers will be 

 equally in demand for all forms of grain-crops. 



These considerations have led me to the conclusion that the geo- 

 logical history of phosphatic deposits should receive more deliberate 

 attention than has yet been given to it. 



When I began my work in the United States Geological Survey, 

 I asked permission of the director to continue my studies on phos- 

 phatic deposits. There was at the time no money available for 

 these studies : it was therefore necessary that they should be car- 

 ried on without other expense to the survey than that involved in 

 the small share of my time which could be given to the supervision 

 of the work. It was my good fortune, however, to find in one of 

 my students of geology. Dr. R. A. F. Penrose, jun., a person who 

 has been willing, at his own cost, to undertake a preliminary study 

 of the whole field as far as our knowledge extends, and thus to 

 prepare the problems concerning American phosphate deposits for 

 detailed inquiry. This work he has pursued with great intelligence 

 and energy during the two years in which he has been engaged in 

 it. In this task he has examined all the known phosphate deposits 

 of the United States and Canada, and has made a careful inquiry 

 into the literature of the subject, as is shown by the extended bib- 

 liography which is appended to his report. 



The object of this work being to make a necessary preparation 

 for the further study of American phosphatic deposits, Dr. Pen- 

 rose's studies were not designed to be encyclopedic in their scope, 

 but rather to afford a synopsis of what is known of the deposits in 

 this and other countries. So little is yet generally known of the 

 several conditions under which these deposits may occur, that it 

 would be very blind work to search for them in this country with- 

 out a careful endeavor to bring together the experience which has 

 been gained in other countries. It will be evident to the reader 

 of Dr. Penrose's report that the workable deposits of pho'sphates 

 are found in a greater variety of circumstances than those which 

 contain most mineral substances that have an economic value. It 

 is not likely that we have as yet exhausted the inquiry into the 

 modes of occurrence of this substance ; but this synopsis of the ex- 

 perience in this and other countries, which is much more extensive 

 than any other which has been published, will, I believe, serve as a 

 guide to the further search for sources of supplies of phosphatic 

 manures. It will also be evident to the reader that the conditions 

 of occurrence of these deposits in Europe make it plain that the 

 search for them in this country m.ay advantageously be directed to 

 many districts in which they have not as yet been found. 



So far, the vein deposits of apatite, such as those which are so 

 abundant north of the St. Lawrence, have not been found in workable 

 quantities within the limits of the United States, though the gen- 

 eral geological conditions of the Laurentian area exist in the Adi- 

 rondack district and in the southern parts of the Appalachian sys- 

 tem, as well as in several districts of the Rocky Mountains. It 

 would be remarkable if extensive deposits of this nature, so common 

 in Canada and in the equivalent rocks of northern and southern 

 Europe, should not be found at many points in our American 

 Archaean formations. It is on this account that so much space in 

 this report is given to the description and illustration of the Cana- 

 dian apatite deposits. So, too, we may hope to find in the ancient 

 rocks of this country deposits analogous to the great Logrosan and 

 Caceres veins in the province of Estremadura, Spain. 



The cretaceous deposits of Belgium (which at the present time 

 are, next after the phosphate beds of South Carolina, the most pro- 

 ductive in the world) present a type of beds the like of which have 

 not as yet been discovered in the United States, though deposits of 

 the same age, formed under about the same conditions, abound in 

 this country. It is not to be expected that phosphatic deposits will 

 exactly repeat themselves in strata of the same age in widely 

 separated regions ; yet it is clear, from the summary" account of 

 the geological distribution of these phosphates in Europe and 

 North America, that in the case of these, as well as in that of other 

 substances of value in the arts, there are certain guiding principles 

 which we may base on the stratigraphy of the deposits to aid our 

 search. The known workable deposits of a phosphatic nature are 

 limited to certain portions of the geological section. Beginning at 



the surface, the deposits now forming these zones are, in descend- 

 ing order, as follows : — 



(i) Superficial deposits, including (a) those formed in the man- 

 ner of guanos ; (/>) the deposits formed in the bottoms of fresh- 

 water swamps, sometimes in connection with deposits of bog iron 

 ore (hematite) ; and (c) deposits which are the result of the long- 

 continued decay of rocks containing a small portion of lime phos- 

 phate intermingled with lime carbonate, as, for instance, the de- 

 posits of North Carolina. This superficial group of deposits has 

 no other common feature save that they are on the surface, and 

 are due to causes now or recently in action. 



(2) Deposits of the tertiary and upper cretaceous. These de- 

 posits are generally the result of re-actions which took place on 

 ancient land surfaces, the phosphatic matter being such as formed 

 in swamp beds or in ablation deposits like those of the Carolinas 

 or of eastern England. Below the level of the cretaceous no im- 

 portant deposits of phosphate have been found in the vast section 

 of rocks which lies between that era and the Devonian horizons. 



(3) In the horizons below the level of the upper Silurian, bedded 

 rock phosphates and apatite deposits occur. These infra-Devonian 

 bedded rock phosphates seem to have derived their phosphatic 

 matter from the animals, brachiopods, and small crustaceans, which 

 separated that substance from the sea insects or other food which 

 the old oceans afforded them. These phosphate-bearing inverte- 

 brates appear to have been particularly abundant in the early pale- 

 ozoic seas. 



(4) Below the level of the Silurian the phosphatic deposits which 

 have been worked probably belong altogether to the class of apa- 

 tites or crystallized lime phosphates, and are probably all new de- 

 posits. They evidently occur through a large part of the Lauren- 

 tian section, though, so far, the known deposits of economic 

 importance are possibly limited to one portion of that vast series of 

 rocks. 



The apparent absence of phosphatic deposits of economic im- 

 portance in the section between the Devonian and the cretaceous is 

 remarkable. It is possible that it may be due to our lack of knowl- 

 edge as to the chemical character of the deposits in those parts of 

 the earth's crust. It is more likely, however, that such deposits do 

 not there exist, owing to the fact that the invertebrate species of 

 animals which secrete phosphatic matter in their skeletons became 

 relatively less abundant in the middle portion of the geological sec- 

 tion ; while the vertebrate species, the birds which accumulate 

 guanos, and the fishes which afford an abundance of bones and 

 teeth to littoral deposits, as well as the mammalia whose skele- 

 tons occasionally form a considerable element in the later deposits, 

 did not begin to contribute phosphatic matter to the rocks until 

 comparatively modern times. 



The absence of phosphatic deposits in the upper paleozoic and 

 lower mesozoic strata is well shown by the fact, that, while in the 

 carboniferous and the triassic beds there are abundant land sur- 

 faces which have been carefully explored, no phosphatic deposits of 

 economic importance have been found in them ; while on the rela- 

 tively very limited areas of the tertiary and cretaceous formations, 

 where old land areas have been explored, a large number of depos- 

 its of beds of nodular phosphate have been found. 



From the facts set forth in Mr. Penrose's report and the unpub- 

 lished results of certain studies on swamps, we may draw certain 

 general conclusions as to the best method of prosecuting the 

 search for unknown deposits of American phosphates. These con- 

 clusions are essentially as follows : — 



First, as regards the superficial and recently formed deposits of 

 phosphates. We are driven to the conclusion that this class of de- 

 posits may reasonably be sought for wherever soft calcareous beds 

 containing a certain amount of lime phosphate have been subjected 

 to long-continued leaching by waters containing the share of car- 

 bonic-acid gas which belongs to all rain-water after it has passed 

 through the mat of decayed vegetation. As long ago as 1S70 I 

 became convinced that it was to the leaching-out of the carbonate 

 of lime by the carbonated water of the soil bed that we owe in the 

 main the concentration of the nodular phosphates of South Caro- 

 lina.' Although it is still necessary to explain many of the details 

 of this process to adapt it to the peculiar circumstances of particu- 



' See Proceedings of the Boston Society of Natural History, xiii., 1871, p. 222. 



