418 Reviews — Mineral Resources of Great Britain. 



monograph on British Graptolites. Part i was commenced in 1901, 

 and now by the issue of part xi, containing title-page and index and 

 23 pages of "Historical Kesearch", their labour, extending over 

 fifteen years, is happily completed. We heartily rejoice with 

 the threefold authors in the consummation of their most difficult 

 task. Of the usefulness of such a great work we prophesy future 

 generations of students of palaeontology Avill arise to bless the authors, 

 and also to support the Society as subscribers. Many too, we trust, 

 will likewise be found to add some good work to further the object of 

 the founders of the Society, namely, "to figui^e and describe every 

 species of British fossil." 



II. — Memoirs of the Geological SuRVEr. 



Special Repoel's on thk Mineral Besources or Great Britain. 

 Vol. VI : llefractory Materials : Ganister and Silica-Bock — Sand 

 for open - hearth Steel Furnaces — Dolomite — Besources and 

 Geology, pp. vi -|- 233, with three maps. London: T. Fisher 

 Unwin. 1918. Price 7s. 6d. net. 



IN this, the sixth volume of the reports on the mineral resources of 

 Great Britain, we have the first part of what promises to be 

 a comprehensive account of refractory materials. The greater part 

 of the memoir is occupied by the descriptions of the raw materials 

 used in silica-brick manufacture. These comprise various rock- 

 types, including quartzite, siliceous sandstone, " Dinas rock," 

 " ganister," " crowstone," etc., and in a somewhat similar fashion 

 the manufactured materials are classified as silica-, ganister-, and 

 Dinas-bricks. Unfortunately, such words as " ganister " and 

 " crowstone " are miners' terms, and, owing to their use being local,, 

 their exact significance is not well defined. The word "ganister" 

 originally applied to the silica-rock on a particular horizon in the 

 Lower Coal-measures of the Sheffield district, has never been 

 satisfactorily defined, and it is doubtful whether the definition given 

 in the memoir settles the question. 



It is impossible to use as the main criterion the geological horizon, 

 as not only does the rock vary in different areas but rocks practically 

 indistinguishable from it are found on other horizons in other- 

 localities. The rock must be defined in terms of its petrographical 

 characteristics, but in order that such definition be generally 

 adopted, it must contain references to those properties which 

 determine the utility of the rock as raw material for silica-bricks. 

 The Geological Survey definition is practically a petrographical 

 description of the typical Sheffield rock, but little attempt is made 

 to take into account the latter consideration. There is no doubt 

 that the chemical composition, size and shape of the quartz-grains 

 and the amount and nature of the impurities are of great importance 

 so far as the refractory properties are concerned, but the distribution 

 of these impurities and the nature of the tliin layers between the 

 grains must also be considered, owing to their probable action as 

 accelerators of the inversion of the quartz to the high temperature 

 forms, cristobalite and tridymite. Owing to the great expansion 



