178 Reviews—Field Analysis of Minerals. 
Professor Joly throws out the suggestion that the rate of transformation 
of uranium may have been in the past more rapid than now. This, 
of course, if it could in any way be demonstrated, would necessitate 
a reduction of the time estimates based on such transformation. The 
suggestion can, however, be tested in another way, for if the rate of 
transformation were formerly more rapid than now, then the amount 
of energy liberated during any given period of the past would also be 
creater than now. That is to say, if the earth has cooled from a high 
temperature such as 1,000° C. at or near the surface, the radiothermal 
energy must have retarded the rate of cooling in the past more tham 
it does now. Under these circumstances, if the earth were able to 
cool at all, it would certainly cool so slowly that its age would be 
much higher than the 1,500 million years required by the accumulation 
of lead. Joly’s suggestion, then, is incompatible with belief in an 
earth originally molten at or near the surface. Since no basement. 
has ever yet been found at the bottom of the geological succession 
that has not been molten at some time or other, the period required 
for cooling down to present conditions must have been even greater 
than that demanded by uninterrupted cooling from a molten state. 
Thus, the assumption that radio-active transformations have not been 
uniform leads to far more serious difficulties than does the alternative 
view that geological processes have not been uniform. 
In his essays on mountain genesis and structure, Professor Joly 
introduces a less controversial subject. He shows that the accumulation 
of sediments leads not only to thermal blanketing of the rocks beneath, 
but also to an additional rise of temperature due to the emission of 
heat from the radio-elements contained in those sediments. In this 
way, thick lens of sediments and the rocks below them become so 
weakened by the rising temperature that when the earth contracts 
they are folded and upheaved by compression, in preference to cooler 
and more rigid portions of the crust. The process is worked out im 
convincing detail, and there canbe no doubt that Professor Joly 
has added to the theory of mountain-building a most significant 
contribution. 
Before closing this review, which by no means covers the whole 
scope of the book, the writer feels that he should express the pleasure 
that he has experienced in reading so admirable a collection of essays. 
The rhythm of life, the majesty of the mountains, the inner secrets 
of the rocks, and the stimulating companionship of nature—all are 
revealed in its pages, and reflected in the beautiful photographs with 
which they are illustrated. Anceue Eee 
IJ.—Fierp Awnatysis or Minerats. By G. D. McGricor. The 
Mining Magazine, pp. 86. 1915. 3s. 6d. net. 
fV\HIS book has been written professedly to meet the requirements 
of the traveller.and prospector, and in keeping with that 
purpose it has been published in a size convenient for the pocket. 
The advantages of a small strongly bound book in the field may 
readily be granted, but when the author, in his ‘‘ Prefatory Remarks 
and Advice’’, recommends the traveller also to take with him Brush 
