Reviews — Our Scientific and Popular Journals. 231 



generally found embedded in the rock-mass, whilst the valuable 

 and most highly prized stones, which come to us from abroad, are 

 rarely obtained from the original matrix, but are usually found as 

 grains or pebbles in ancient or modern alluvial deposits, the more 

 perfect and solid ones only having resisted the wear and tear to 

 which they have been subjected since they were set free by the 

 breaking up of their parent rocks. Hence the comparative aljund- 

 ance of the precious stones in the river-valleys of India, Ceylon, 

 Australia, and South America, which traverse the metamorphic 

 strata in which these minerals were originally imbedded. 



Of the gems and precious stones found in Great Britain, by far 

 the largest class are compounds and varieties of silica, which owe 

 their beauty as gems, in many instances, to the presence of an in- 

 finitesimal quantity of some metallic oxide, as manganese, iron, 

 chromium, etc., thus producing those beautifully coloured stones, 

 the emerald, amethyst, cairngorm, etc., so extensively used in 

 jewelry. 



In speaking of the Beryl, at page 130, we observe a misprint, 

 which might, if passed over, mislead the reader. It is there stated 

 that " Beryl is harder than Topaz." On referring to the " Table 

 of Physical Characters of Gems," given on page 133, however, we 

 find their relative hardness correctly stated thus (placing the hardness 

 of the Diamond at 10) : — Topaz = 8 ; Beryl = 7*5. 



This article will be found most instructive, both historically and 

 mineralogically — the Chromolithographic plate which accompanies 

 it is not, however, so good in its way as those to " Reynaud's 

 Histoire Elementaire des Mineraux Usuels" (see Geol. Mag. Vol. 

 IV. 1867, p. 555). 



II. The Quarterly Journal of Science (No. 28) for April, par- 

 ticularly recommends itself to our notice by a most valuable 

 paper by Professor Dr. G. Zaddach, of Konigsberg, on " Amber, 

 its Origin and History, as illustrated by the Geology of Samland " 

 (Prussia). The age of the " Glauconitic sand " deposit, which yields 

 this interesting and valuable fossil Eesin, is of Eocene or Lower 

 Oligocene age, according to Mr. C. Mayer, of Zurich ; but the 

 associated fossils are marine Mollusca, Echinoderms, and Polyzoa ; 

 and the Amber is usually, more or less, rounded and water- worn, 

 the associated fossil-wood being generally only found in small pieces 

 apparently half- decayed at the time of their deposit. Dr. Zaddach 

 devoted himself therefore to the task of ascertaining the probable 

 position of the old land-surface, upon which the Amber-pines grew, 

 that furnished this rich deposit, yielding, on an average, ^-Ib. to lib. 

 of Amber to every cubic foot of sand. Searching for and examining 

 with care all the pebbles and fragments of rock which occur in the 

 ''' Amber-earth," and tracing these to the parent-rock, he shows that 

 the Tertiary " Glauconitic sand " has been formed out of the waste 

 of the Greensand where that deposit reposed on old Silurian rock 

 and he traces the derivation of both the Silurian pebbles and Green- 

 sand to the waste of the old high lands of Northern Europe, con- 



