554 Chronicles of Science. [Oct., 



riably betokens the absence of the other. Our author has, however, 

 proved the co-existence of these species in the disintegrated procUict 

 of certain volcanic rocks of the Palatinate, and also in an uude- 

 composed rock, formerly termed gabbro, but which he now pro- 

 poses to distinguish under the name of Falatinite. He is then led 

 to a discussion of the ordinary laws of association among rock- 

 forming minerals ; and although he does not say very much that 

 is original on this subject, it is nevertheless useful to review such 

 a collection of facts as those whicli he has here brought together 

 for the purpose of disproving most of the commonly-accepted con- 

 clusions. Thus he exposes the fallacy of the famous " law of the 

 felspars" — a law which, as most geologists know, teaches that the 

 alkali-bearing felspars — orthoclase, oligoclase, and albite — are 

 never associated with the lime-felspars — labradorite and anorthite. 

 One argument against this law might be found in the recent views 

 of Tschermak on the constitution of the felspar-group, by which 

 the so-called species, oligoclase and labradorite, are regarded as 

 nothing more than isomorphous mixtures of the two extreme 

 types — anorthite and albite. IMoreover, as a matter of fact, Las- 

 peyres has himself pointed out the existence of a lime-and-soda 

 felspar, closely related to the labradorite type, in certain basaltic 

 lavas of the Lake of Laach, where orthoclase had previously been 

 found. In like manner, sanidine — a variety of orthoclase — occurs 

 with anorthite in the andesite of Nagy-Banya. 



This example must suffice to show the kind of evidence with 

 which our author sweeps away many a long-cherished notion ; but 

 it may please those who cling tenaciously to the old articles of 

 faith to know that, in spite of the progress of science, a few of the 

 petrographical laws still hold their ground ; such, for instance, as 

 the absence of white potash-mica from the younger eruptive rocks. 



So much interest naturally attaches to anything bearing on the 

 history of those strange visitants from extra-terrestrial regions, 

 which occasionally reach our earth in the form of meteorites, that 

 no apology is needed for calling attention to an excellent resume 

 of our knowledge on this subject, lately published by M. Stanislas- 

 ]\Ieunier.* Most of our readers know that meteorites arc divi- 

 sible into two great groups — meteoric stones and meteoric irons. 

 The members of the former class are composed of a stony base, 

 consisting of a complex mixture of various magnesian silicates, only 

 partially attacked by acids; those silicates which have the com- 

 position of olivine being decomposed, whilst others, resembling 

 hornblende and augite, are left intact. Throughout this base of 

 sihceous minerals, numerous grains are usually disseminated in 

 greater or less number, some of which are metallic, and consist, 



* '• Rcclierclics siir la composition et la Structure dcs Meteorites : " ' Aunales 

 de Chimic ot do PbyBiquc,' seric iv., tome xvii. p. 5. 



