Reviews — Mineral Resources of Great Britain. 419 



during these inversions, the best rocJi, other things being equal, is 

 that in which as much of the quartz as possible can be transformed 

 during manufacture and which therefore will show the smallest 

 after-expansion in use. It is improbable that a really satisfactoiy 

 definition will be obtained until more is known concerning the 

 petrological properties which determine the usability of the rock. 



In the introductory chapter an account of the manufacture of 

 silica-bricks is given, and this, considering its condensed nature, 

 is satisfactory except with regard to the temperatures to which the 

 bricks are fired. It is stated, for example, that in North Wales 

 these range from cone 16 to cone 29, but these figures are much 

 higher than those attained in general practice. It is very doubtful 

 Avhether first-grade silica-bricks are ever fired in this country at 

 temperatures above cone 16, and this can be verified by a comparison 

 of liritish and American bricks. The latter are rarely fired above 

 cone 17 or 18, and, even taking into account the more prolonged 

 firing, the much smaller proportion of unconverted quartz which 

 they contain, in comparison with the former, can only be explained 

 by the lower temperature to which the British bricks have been 

 subjected during firing. 



The major portion of the memoir is taken up by an account, with 

 details of the occurrence, methods of working, reserves, etc., of the 

 mines and quarries in which siliceous rocks are obtained, short 

 petrographical descriptions of the rocks being appended. The 

 qualitative nature of the latter militates against the utility of the 

 results. It is greatly to be regretted that practically no chemical 

 details are given and also that the refractory tests mentioned in the 

 preface as having been carried out are deferred, apparently to a later 

 volume. These data would have been much more useful if the}^ had 

 appeared with the descriptive part. The latter seems to be fairly 

 accurate and detailed so far as the materials already being worked 

 are concerned, but the information regarding untouched English 

 sources is very meagre, though there is a chapter on "potential" 

 Scottish supplies. 



In a chapter devoted to an account of the sand and clay pockets 

 of the Peak District, the geological age of the deposits is given as 

 possibly " post-Triassic and pre-Glacial", Avhile in a table earlier in 

 the volume they are chai'acterized as "post-Glacial". As a matter 

 of fact, the post-Triassic age of some of these deposits cannot be 

 regarded as definitely proved. 



The remainder of the volume describes the British deposits of 

 sand suitable for open-hearth steel furnaces, and of dolomite for 

 lining converters, the beds of open-hearth furnaces, etc. In con- 

 nexion with the paragraph on the decalcification of dolomite, some 

 recent work on the Grenville (Quebec) deposits may be noticed. 

 Where the material is a mixture of magnesite and dolomite, it is 

 possible to increase the proportion of magnesia by "slaking" the 

 calcined minerals, but it has not been found possible to vary the 

 proportions of lime and magnesia by this method in dolomite alone. 



The editing of the collected information has, as usual, been well 

 done, though a few misprints occur : for example, the spelling 



