Corresp07ide7ice, 3^5 
are probably analogous to the changes going on in what we call the 
organic world, and that the changes go on with almost the same ease 
and rapidity as they do in the organisms. 
Although there is little said regarding the classification of ore de- 
posits, professor Van Hise's paper has an important bearing on this 
phase of the general theme. 
When professor Van Hise sums up the situation and says that a 
"Complete theory for many ore deposits must be a descending, later- 
al-secreting, ascending theory," it is certainly a conclusion from which 
there is no escape. We can only attain an adequate explanation of ore 
deposition by considering all of these currents, sometimes working 
independently perhaps, but usually operating in conjunction and 
practically contemporaneously. 
In order that any classification of ore deposits may be made use- 
ful to the fullest extent it must first of all be simple; second, it must 
be capable of being readily applied in the field; and third, it must be 
a guide to proper exploitation. No matter how refined and well- 
fitting a scheme we have, if it does not meet these three requirements 
it will not be adopted or even be considered by practical men. 
The closing paragraphs of the paper are devoted briefly to the 
bearing of the principles set forth, upon ore classification, and espec- 
ially a plan that is genetic. How far such a scheme can be made 
successful professor Van Hise does not indicate in this connection. 
The experience of the past would go to show that a purely genetic 
plan, that is at the same time a useful one, is not practicable, nor 
can ever get beyond the stage of being genetic in name only. 
It is possible to have a genetic scheme of classification for the 
rocks that will aid in their consideration because those who have most 
to do with them are able to approach them from a strictly scientific 
and philosophic standpoint. With the ores this can never be so, be- 
cause the vast majority of ore students are trained from a wholly dif- 
ferent standpoint. 
If we begin on the basis of the genetic rock classification, to ar- 
range ore deposits we, of course, have our first grand sub-divisions 
determined directly by origin, whether (i) igneous, (2) sedimentary, 
or (3) deposited by underground waters. From the standpoint of ores 
as ore bodies, the first and second great groups have in reality very 
subordinate taxonomic ranks, possibly so low as the fourth order. 
The third, comprising practically all ore deposits, is a general agency, 
and therefore cannot be considered among the criteria of classifica- 
tion at all. 
As in the case of other natural objects, ores have many different 
viewpoints from which they must be considered. We can classify 
them according to the standards of each of these standpoints, and we 
would have as many different schemes of classification. Theoretically 
we should consider each according to its value, and erect a general 
scheme embracing all. In practice we can only give prominence to 
