520 A. G. MacGregor and F. R. Ennos — 



Sodalite. — Mr. Player's analysis of Traprain Law, given in 

 Dr. Hatch's Edinburgh Koyal Society paper (5), does not record 

 chlorine. 



Rosenbusch states (13, p. 963) that in the phonolitic rocks the 

 minerals of the haiiyne group (which includes sodalite) are always 

 idiomorphic. The mode of occurrence of sodalite in Traprain Law 

 constitutes an exception to this rule. 



The only other known occurrence of sodalite in a rock from the 

 British Isles is — as far as I am aware — that noted by Dr. Shand 

 in his paper on borolanite and its associates in Assynt (14). Here, in 

 a rock which he calls assyntite, he found idiomorphic sodalite, 

 showing sections of the rhombic dodecahedron, and enclosed by all 

 later minerals. He identified the mineral by its low refractive 

 index and isotropism, and by the chlorine reaction of the rock. 

 He says there is no evidence to justify calling the mineral haiiyne 

 or nosean in preference to sodalite. The rock reacts strongly for 

 chlorine and only very faintly for sulphuric acid. An analysis of 

 assjrntite has been published by Mr. A. Gemmell (3). 



Olivine. — References to the occurrences of olivine in phonolites 

 will be found in Rosenbusch's classical work (13, pages 968, 969, 

 974) and in the bibliography on pages 952 et seq. of the same 

 volume. I have consulted the papers by A. von Lasaulx (7), by 

 H. Mohl (10), and by P. Marshall (9) therein mentioned, but in no 

 case could I find a record of ophitic olivine. 



Lady McRobert (8) describes an augite-olivine-trachyte from the 

 Mid Hill, Eildon Hills, where the olivine is represented by occasional 

 yellow and red-brown pseudomorphs. She says the rock closely 

 resembles that of Traprain Law, but although expecting to find 

 nepheline in the Mid Hill rock, she could not detect it by optical 

 or microchemical methods. 



Appendix II. 

 The Historical Interest op the Traprain Law Phonolite. 



Traprain Law has considerable interest in petrological history, 

 as it was, I believe, the second instance in which nepheline was found 

 in a " Palaeozoic volcanic rock ",i and it therefore formed one of the 

 important links which strengthened the chain of evidence, proving 

 that there is no essential difference between the so-called palseo- 

 volcanic and neovolcanic rocks of the continental geologists. 

 0. A. Derby (2) discovered in Brazil the first known occurrence of 

 nepheline and leucite in palaeozoic volcanic rocks. 



Rosenbusch's examination of Derby's and Hatch's Palaeozoic 

 phonolites must have convinced him that he had been right in saying 

 in the 1887 edition of bis textbook (11), that to geological age 

 there had previously been attributed a more important influence on 

 the structural and mineralogical forms of 'eruptive rocks than was 



1 " Palaeovulkanisches Gestein." The fact that the Traprain Law phonolite 

 is actually an intrusion does not affect the argument. 



