554 Notices of Memoirs — J. J. H. Teall — Igneous Magmas. 



Jackson-Harmswortli expedition in Franz Josef Land, recently 

 examined by the author and Mr. E. T. Newton, are many basalts 

 essentially composed of labradorite, augite, and interstitial matter, 

 in which labradorite formed first, then augite, and last of all the 

 interstitial matter, either with or without further differentiation. 

 The main interest of these rocks lies in the composition and relations 

 of the interstitial matter. This is occasionally present as a deep 

 brown glass, but more often is represented either by palagonite or 

 by a turbid and more or less doubly refi'acting substance crowded 

 with skeleton-crj'stals of magnetite. In many specimens it is only 

 in this form that the magnetite occurs, the labradorite and augite 

 being free from inclusions of this mineral. These facts prove that 

 magnetite may belong to a very late stage of consolidation, and that 

 progressive crystallization may lead to a concentration of iron-oxides 

 in the mother liquor. 



The palagonite appears to have been formed by the hydration of 

 a deep-brown glass. An analysis was made of it with the following 

 results : — 



I. II. 



Silica 



Titanic acid ... 

 Alumina 

 Ferric oxide ... 

 Ferrous oxide ... 

 Lime ... 

 Magnesia 

 Soda ... 



Potash 



Loss on ignition 



99-54 100-00 



In the second column the water is neglected, and the percentage 

 composition of the remaining substances indicated. The analysis 

 confirms the view that a great concentration of ii-on-oxide has 

 taken place, and suggests the further conclusion that there has 

 been a concentration of magnesia and a reduction of the lime, 

 silica, and alumina, thus agreeing with the results of the microscopic 

 examination. 



Several observers are quoted by the author as having established 

 the fact that magnetite is not always one of the earliest minerals to 

 form, and in basalts of the Franz Josef Land type there is clear 

 evidence that a basic magma may consolidate without any separation 

 of this mineral, although the mother liquor may contain 30 per cent, 

 of iron-oxides. 



Brogger, Vogt, and others have observed a tendency in certain 

 dykes for the molecular groups of which the first-formed minerals 

 are built to migrate towards the cooling margins. The cases 

 examined are mostly those of intermediate rocks, in which the 

 basic minerals are the first to form, so that the margins are more 

 basic than the central parts. But it appears probable that cases 

 occur in which the opposite is true. If the magma of the Franz 



