:?(>:> Tin American Geologist. May. i sm 
iliis. Three sentences below the one quoted I state thai there are ;i Few 
ores belonging to this group; but, notwithstanding this, he says thai I 
have "evidently overlooked" certain silicate ores, which, however, are 
all described in their proper place in my book, — calamine on pages 23 
ami 343; garnierite on pages 292 and 294; and chrysocolla on pages 22 and 
208. 
Next, quoting me as follows: "Sometimes, though not commonly, 
gold occurs in iron pyrites in invisible grains," he says, "it is almost 
unnecessary to say thai oi f the most common modi's of occurrence 
of gold is in intimate association with iron pyrites, so that this state- 
ment is extremely misleading," Not so misleading, I venture to say, as 
his criticism. On page 169, when speaking of gold, I say just what he 
does, but, although there is nothing in the quotation nor in his remark 
to indicate it. the sentence- quoted by him was from a paragraph on 
iron pyrite. The common occurrence of gold is in pyrite; bul is gold 
common in pyrite? 
II is criticism of m\ statement that native gold is the "typical occur- 
rence and the one from which the gold in use is obtained*' is a criticism 
on my "good language." I had just spoken of the telluride as an ore, 
and it isevidenl that I meant the gold "••>• a whole, not "//of the gold. 
His object ion to my speaking of chalcopyrite as a combination of iron 
and copper sulphides in varying proportions, and of siderite as a simi- 
lar combination of iron carbonate (the latter word being omitted by mis- 
take) and calcite. depends upon his misinterpretation of the meaning of 
the word combination, which he assumes to mean chemical combination. 
That I recognize the fact that the mineralogical chalcopyrite and sider- 
ite are definite chemical compounds is shown by the fact that [gave 
i heir formuhe. Since I was not writings text-book on mineralogy I did 
not feel called upon to introduce and explain isomorphous mixtures and 
replacements. 
Excepting by hazarding a guess, Dr. Penrose does not appear to be 
able to understand what I mean by ••mineralized ores.*' My meaning is 
explained on pages 15 and 16 of the book. Nor is it quite clear to him 
what I mean by •"rust." Rust is oxidation and iron rust is the product 
of oxidation of iron, while lead rust is the similar product for lead. 
The pale yellow rust of lead, towhich I refer and which he questions, is 
used by the prospectors of the west, oral least by some with whom I 
have been in the field in Montana, as a sign of lead. 
The reviewer cannot understand on "what basis" an author has "mod- 
ified" the geological sections of other authors. In the instance under 
consideration, as in others (and always with a statement of ii). the sec- 
tions were modified for the purpose of rendering them more diagram- 
matic, so that the beginner could understand them. The modifications 
were made for exactly the same reason that their technical descriptions 
wen' modified. 
We are told thai the book "bears evidence of a lack of the sense of 
proportion in t he amount of space given to di lie rent subjects." It would 
have been more modest lo have said that this seemed so to the reviewer. 
