126 H. S. JEVONS, H. I. JENSEN AND C. A. SUSSMILCH. 



solutions of silicates at a very high temperature, possibly- 

 above the critical temperature, and thus highly fluid, if 

 not actually gaseous. The very coarse pegmatites might, 

 indeed, be regarded as crystallised from the mother liquor 

 of the more normal pegmatites just mentioned ; because 

 the latter would be deposited first, and from the outwardly 

 passing hot solution, and thus nearer to or within the mass. 



Part II. Explanation of the Differentiation Phe= 

 nomena of the Prospect Intrusion. 



By H. I. Jensen and O. A. Sussmilch. 



The features of the Prospect Intrusion explainable by 

 one or more of the differentiation hypotheses outlined in 

 Part I, are 



1. The Banded Nature of the Intrusion as a whole. 



2. The Segregation Veins. 



3. The Sub-alkaline nature of the whole intrusion. 



1. The Banded Nature of the Intrusion. 



A full description of the variation in mineral composition 

 of the Prospect essexite appears in our previous paper (p. 

 513). It was shown that there was a progressive change 

 in mineral composition from the upper margin of the intrus- 

 ion down to a depth of about 65 feet, while below that 

 depth the essexite was, as far down as it is exposed, of a 

 uniform composition. As a result of these variations the 

 upper part of the intrusion is divided into definite layers 

 as follows : — 



Depth below Thick- 

 top, ness. 

 (Metres.) (Metres.) 



A. Pallio-essexite 1-4 4 



(a) Essexite 4-13 9 



(b) Upper segregation vein 



(c) Essexite 13-17 4 



(d) Lower segregation vein 



(e) Essexite 17-19 2 

 O. Essexite, normal phase 19 k i D ^) 



B. Essexite, 

 felspathic phase 



