Notices respecting New Books, 65 



Silica 57'45 



Alumina 17-41 



Protoxide of iron 8'55 



Oxide of magnesia traces 



Lime 4-63 



Magnesia (difF. ) 2'05 



Soda 2-34 



Potash 3-69 



Water and loss by ignition 3'88 



100-00 



It contains no carbonates ; so that they have been destroyed by the 

 metamorphism — but slowly, since the calcareous body of a Belemnite 

 had been changed into a paste of petrosilex which preserved the 

 structure. The lime had not been entirely removed, a part at least 

 remaining as a hydrosilicate. If Dr. Apjohn's analysis be a good 

 representation of the normal lias, we see, since it contains no 

 alkalies, that the altered lias had gained 6 per cent, of them. The 

 occurrence of potash is remarkable, and is j)robably connected wth 

 that of the apophyllite, which is a zeolite having the composition 

 KO, -2 SiO^ + 8 (CaO, SiO^) + 1 6 HO. 



The proportion of silica is small for its name of " flint-slate," but 

 is greater than that possessed by basalt. It is but little for a jasper, 

 but is more than that usual in clay. 



Lastly, iVI. Delesse, admitting that the presence of black volcanic 

 augite indicates a great heat, maintains that the occurrence of 

 zeolite in such large quantity demonstrates the presence of water 

 or aqueous vapour, and proves that the metamorphism of the lias 

 was due to an action at once igneous and aqueous. 



Our space will not permit us to mention more of the numerous 

 examples of this part of the subject which the book contains. 



M. Delesse gives a number of details respecting the alteration of 

 the intrusive rock ; but in looking over these we have been struck 

 by the difficulties of the investigation. It must generally be con- 

 ducted by examining one specimen from the heart of the intru- 

 sive rock, and another from the margin where it is near the in- 

 cluding rock, and comparing the difference of the two. But it must 

 necessarily follow that near the junction of the two rocks each is 

 more likely to be " weathered " or acted upon by the infiltration of 

 water, &c., than at a distance from that junction. The very line of 

 division between the two gives access to the atmospheric influences. 

 It becomes, then, exceedingly difficvdt to distinguish between the 

 alteration produced by mere " weathering" or infiltration, and that 

 received by the intrusive rock from the reaction of the adjacent rock 

 at the period of intrusion. It is only where the whole mass of one 

 part of an intrusive rock differs from the whole mass of another 

 part, the two jjarts being surrounded by rocks of a different ciiarac- 

 ter, that we can be sure that the dift'erence arises from tliat source. 



The observat.ons of Prof. Haughton on tlie granite of the Mourne 

 Mountains and 'the neighbourhood, form the best, if not the only good 



Phil. May. S. 4. Vol. 18. No. 117. My 1859. F 



