Alexander Scott — The Crawfordjohn Essexite. 513 



as having been Indo-European and coming by the 'eastern way', 

 a view which none the less is still generally held in Scandinavia. 

 But it is plain that, if the western way of migration to the north was 

 still used as late as the time of the long barrows, so much the more 

 probably was it that road which was used during the preceding stage 

 of the kitchen-middens. 



The end of my task is now reached. Within the limits of Great 

 Britain the Ice Age can be followed from its beginning to its end. 

 England has the further advantage of having already possessed quite 

 a numerous population before the Ice Age, and has been inhabited 

 ever since. Archseology can therefore lend a strong support to 

 glacial geology. It was these fortunate English conditions which 

 originally gave me the idea of attempting this brief general synopsis 

 of the course of the Ice Age in this country. I cannot, however, lay 

 down my pen without expressing my hearty thanks, in the first place 

 to England, which, in the midst of this world-war and general 

 disturbance, has given me a calm and peaceful lodging from the very 

 beginning of the war, when I came here headlong, down to the 

 present when I return to my Eatherland ; and also to my English 

 friends, new and old, unnamed but unforgotten, who have lent me 

 a hand and facilitated my geological studies in England. 



Y. — The Crawfordjohn Essexite and Associated Bocks. 



By Alexander Scott, M.A., B.Sc. 



{Concluded from the October Number, p. 461.) 



ANOTHER type, which is found in both quarries and which under 

 the microscope has the aspect of a monchiquite or limburgite, 

 probably represents the actual marginal rock of the intrusion. 1 It 

 consists of small microphenocrysts of augite and olivine in a dark 

 matrix, which can be resolved into granular augite and magnetite in 

 a nearly isotropic base. The latter, which sometimes contains 

 felspar microlites, seems to be mainly analcite with some nephelite, 

 as it can be readily gelatinized and stained, while the refractive 

 index is very low. The felspar microlites are small and sometimes 

 have a rough trachytic structure resembling that of the mugearites. 

 Following Harker's suggestion that augite-olivine rocks with an 

 isotropic base should be classed as limburgites when the base is glass 

 and as monchiquites when it is analcite, 3 this rock can be included in 

 the latter group. The parts which are richer in felspar may be 

 termed analcite-basalts. 



A sample of monchiquite from the large quarry has been analysed, 

 and the results are given in column 1, table iii. The rock does not 

 differ much in chemical composition from the essexite. The silica 

 content, however, is noticeably lower, while the amounts of iron 

 oxides and alumina are slightly higher. While the amounts of 

 augite in the two rocks are probably very similar, the increase in 

 magnesia and ferrous oxide in the monchiquite, coupled with the 

 lower silica-content, indicates a greater proportion of olivine. 



1 This rock was first brought to my notice by Mr. W. K. Smellie. 



2 Petrology for Students, 4th ed., 1908, p. 158. 



DECADE VI. — VOL. II. — NO. XI. 33 



