10 DEPOSITS OF PHOSPHATE OF LIME. [bull. 46. 
portance 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 geolog- 
ical history of phosphatic deposits should receive more deliberate atten- 
tion than has yet been given to it. 
When I began my work in the U. S. Geological Survey, I asked per- 
mission of the Director to continue my studies on phosphatic deposits. 
There was at the time no money available for these studies; it was 
therefore necessary that they should be carried on without other ex- 
pense 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, jr., a person who was willing at his own cost to under- 
take a preliminary study, of the whole field as far as our knowledge ex- 
tends 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 in- 
quiry into the literature of the subject, as is shown by the extended 
bibliography which is appended to this report. 
The object of this work being to make a necessary preparation for 
the further study of the American phosphatic deposits, Dr. Penrose'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 without 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 phosphates are found in a greater variety of circumstances 
than those which contain most mineral substances that have an eco- 
nomic 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 experience in this and other countries, which is much more exten- 
sive than any other which has been published, will, I believe, serve as a 
guide to the further search for sources of supplies of phosphatic ma- 
nures. It will also be evident to the reader that the conditions of oc- 
currence of these deposits in Europe make it plain that the search for 
them in this country may 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 abun- 
dant north of the St. Lawrence, have not been found in workable quan- 
tities within the limits of the United States, though the general geo- 
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