Correspondence — Avanturine Quartz. 535 



with a rich source of phosphate of lime of organic origin, for manure, 

 the remnants of faunas of Secondary and Tertiary age, for the 

 utilization of which we are indebted to the Eev. Prof. Henslow, and 

 which may be referred to specially, as an instance of the practical 

 application of Geology to the benefit of agriculture. 



The relation of Geology to Agriculture forms, of itself, a most 

 interesting chapter of this book; it is a subject of the greatest 

 national importance, and we are glad to know that the Government 

 Geological Surveyors are also becoming convinced that the super- 

 ficial deposits are deserving of their attention and mapping. 



The present book contains : Part I. " The Natural History of the 

 Eaw Materials of Commerce."— Part II. " The Commercial Pro- 

 ducts of the Vegetable Kingdom." — Part III. " The Commercial 

 Products of the Animal Kingdom."— Part IV. "Raw Mineral Pro- 

 duce;" and, lastly, an Appendix, containing a Vocabulary of the 

 Names of Natural Productions, in the Principal European and 

 Oriental Languages. The Geographical Distribution of Food and 

 Industrial Plants is illustrated by a small coloured map, showing the 

 Botanical Zones of the world. 



Dr. Yeats announces that the present volume will be followed by 

 "The Industrial and Political History" and by "The Technical 

 History " of the same subject. 



Among the list of contributors to the present volume we observe 

 the name of Mr. Ealph Tate, F.G.S., F.L.S., a good guarantee for 

 the careful execution of the geological part of the volume. 



We heartily wish the author and his book all possible good, and 

 trust that the future volumes may turn out as agreeable and readable 

 as the present one. 



coK;iaEs:poisriD:E3isro:E3. 



AVANTURINE QUAETZ IN BRITAIN. 



SiE,— In the Geol. Mag. for Sept., p. 444, you announce that Mr. 

 G. W. Traill has discovered " Avanturine Quartz" in Orkney, on the 

 shores of Inganess Bay. It is spoken of as " a scarce variety of quartz," 

 but it is really not a scarce mineral, nor is it a variety of quartz, but 

 only ordinary quartz inclosing scales of mica. It is commonly met 

 with in micaceous sandstones all over the world, and has no more 

 right to a distinctive title than a quartz crystal containing any other 

 foreign body entangled in its mass. B. J. R. 



London, Zrd Sept., 1870. 



ARCHDEACON PRATT ON THE INTERNAL FLUIDITY OF THE 



EARTH. 

 Sir.— All Geologists must rejoice to see a question of such interest 

 as that of the Internal Fluidity of the Earth discussed in the 

 pages of the Magazine by authorities like M. Delaunay and Arch- 

 deacon Pratt. I confess that M. Delaunay's arguments, as given to 

 us by Mr. David Forbes,^ staggered my faith in Mr. Hopkins's 

 1 Geological Magazine, vol. v., p. 511. 



