ELEMENTARY GEOLOGY, ETC. 23 



Page 219. The oxide of copper which enters into the composition of 

 Azurite is called " oxide of copper, 70 per cent ;" while, in the same page, 

 the oxide of copper entering into the composition of Malachite is described 

 as " Deutoxide of copper, 70.5 per cent." We are at a loss to understand 

 this difference in names, as the oxide is the same in both cases, viz. CuO. 



In page 223, the error respecting Hornsilver, already noticed, is re- 

 peated, although the correct atomic weight of silver is given in the table? 

 page 9. Mistakes of this kind arise from the indiscriminate copying by 

 incompetent hands from the works of others, as this formula AgCl, 



2 



may be justified by writers who adopt 216 for the atomic weight of silver, 

 which is double that used by Professor Ansted, viz., 108. 



By far the most serious difficulty to the student in this Mineralogy is 

 likely to arise from the confused and sometimes inaccurate use by Professor 

 Ansted of both the Chemical and Mineralogical formulae of Minerals. This, 

 also, we suspect, arises from his having extracted his information from 

 various sources, and transferred it quite undigested to the pages of his own 

 book. In some instances, where we can recognise a literal translation, he 

 has transferred errors and truth together, and given them equal pro- 

 minence, to the serious detriment of his inexperienced readers. 



Notwithstanding the errors we have pointed out, we believe that the Phy- 

 sical Geography and Mineralogy, although at present inferior, are capable, 

 by a careful revision by a thoroughly competent hand, of being made equal 

 to the rest of the book. Professor Ansted is evidently more familiar with 

 Descriptive Geology and Mining operations practically than he is with the 

 Mechanical considerations requisite in Physical Geology, and the Chemical 

 knowledge, without which no real progress can be made in Mineralogy. 



We are of opinion that on a subject like Geology, of a practical charac- 

 ter, no man can write well who does not himself possess a practical know- 

 ledge of the particular branch he treats of; and hence, we believe, can be 

 explained the unequal character of Professor Ansted's book. 



DESCRIPTIVE GEOLOGY. 



The statement of the preface that the Descriptive Geology has been " en- 

 tirely re-arranged, and for the most part re-written" is only accurate when 

 applied to the last three chapters of this part of the book, as the first three 

 chapters are almost identical with those of the first edition. In fact, the 

 original plan of the book, which tied down the author to write so as to suit 

 second-hand illustrations borrowed from Beudant's " Cours Elementaire de 

 Geologie," almost precluded the possibility of alteration or improve- 



