214 ReGicws— Traill on Quartz and Opal. 



especially as the breaks in England are more numerous, and the 

 formations less abundant than in America. Until the discovery of 

 Nos. 8 to 11, no one suspected that the pal^ontological break between 

 7 and 12 was of any consequence. Now, it appears that this break 

 in New York represents three or four large groups of strata 600 to 

 800 miles away. Much more, therefore, may a break in England 

 represent a formation in America, and vice versa. 



Singularly enough the establishment of a zone of life below the 

 Potsdam of America is, in agreement with the views of Professor 

 Emmons, who as long ago as 1842 maintained the existence of a 

 system which he called Taconic, and correlated it with the Cambrian 

 of England. A part of the strata included in Mr. Billings' Lower 

 Potsdam were labelled Taconic by Emmons twenty years ago. Al- 

 though many of the so-called Taconic strata are unequivocally Lower 

 Silurian, the question seriously presses upon us whether Nos. 14 and 

 15, with perhaps other formations connected with them, ought not 

 to be called Taconic at the expense of both Silurian and Cambrian. 



II. — An Elementary Treatise on Quartz and Opal, including 



THEIR VARIETIES, ETC. By GeORGE WiLLIAM TrAILL, G.S.E. 



Edinburgh : Maclachlan and Stewart. London : Simpkin, Mar- 

 shall and Co. 



'HY this little book has been published we are at a loss to con- 

 ceive, as it is not written in a popular manner, nor does it fill 

 any gap in mineralogical literature. Students of mineralogy will 

 find in the several manuals on this subject, already published, all that 

 is to be found in this work ; and, indeed, in some of them, much 

 more. In his Preface, the author says that quartz and opal hold a 

 prominent place in most collections, and are well suited to form 

 an independent treatise. We agree with him, provided always 

 that the treatise includes a complete epitome of all the investi- 

 gations that have been made ujDon the subject up to the time of 

 its publication. But in this book no mention is made of the re- 

 sults of the very complete studies of M. Des Cloiseaux upon the 

 crystallography and other physical properties of this mineral, which 

 is to be found in his " Manuel de Mineralogie," the first part of 

 which was published in 1862 : and more in detail in Vol. xlv. 

 of the "Annales de Chimie et de Physique," and in various me- 

 moirs presented to the Academy of Sciences of Paris ; nor to the 

 researches of Dr. E. Weiss on the crystallisation of quartz — all of 

 which would have afforded materials for some very instructive 

 chapters. The former eminent mineralogist has arrived at the con- 

 clusion that a simple crystal of quartz is of very rare occurrence. 

 He shows that the apparently simple crystals from Buxton in Derby- 

 shire, Dauphine, Traversella, and other localities, are really macles. 

 The important phenomena of circular polarisation, so peculiar to 

 quartz, and the curious structure of amethyst, the author dismisses 

 in a few sentences, while the interesting varieties called right and 

 left handed quartz arc not even mentioned. The various minerals 



