382 Reports & Proceedings—Geological Society of London. 
tooth. The specimen, which represents a new species, was obtained 
‘by Mr. H. H. Freer from shale below the Rough Rock, in the 
upper part of the Millstone Grit, at Brockholes, near Huddersfield, 
and was presented to the Museum of Practical Geology by Mr. E. 
Crowther. 
2. “The Tertiary Volcanic Rocks of Mozambique.” By Arthur 
Holmes, B.Sc., A.R.C.Sc., D.I.C., F.G.S. 
Until recently the district of Mozambique—geographically as well 
as geologically—was one of the least known of the Kast African 
coast-lands. During the seasons 1910-11 a prospecting expedition 
was organized by the Memba Minerals Ltd., and during the second 
season Mr. E. J. Wayland, Mr. D. A. Wray, and the author visited 
the country as geologists to the Company. 
With the exception of a coastal belt of Cretaceous and Tertiary 
sediments, flanked on the west by later Tertiary volcanic rocks, the 
whole territory consists of a complex of gneisses and other foliated 
rocks, intruded upon by granites belonging to at least two different 
periods. From Fernao Vellosa Harbour to Mokambo Bay the junction 
of the sedimentary formations with the crystalline complex is a faulted 
one, and the volcanic rocks, now greatly dissected by erosion, are 
distributed on each side of the fault. The lavas are of post-Oligocene 
age, and are clearly the result of fissure eruptions, the feeding 
channels being exposed as numerous small dykes that penetrate the 
underlying rocks. 
Throughout the area the prevailing lavas are amygdaloidal basalts, 
in which the chief amygdale minerals are chlorite, heulandite, and 
forms of silica. An andesite dyke of later date occurs near the 
Monapo River. In the north, near the Sanhuti River, picrite-basalt, 
basalt, phonolite, and sdlvsbergite have been found, and related lavas 
occurring elsewhere in the area are tephritic pumice and egirine- 
trachyte. Thus, there occur together, within the limits of a small 
voleanic field, series of both ‘ alkali’ and ‘ cale-alkali’ types of lavas. 
The ‘alkali’ series can be closely matched by the lavas of Abyssinia, 
British East Africa, Réunion, and Tenerife. The amygdaloidal 
basalts of the ‘cale-alkali’ series are similar to those of the Deccan, 
Arabia, and East Africa, and also to those (of late Karroo age) 
occurring in South Africa and Central Africa. 
In all, ten analyses have been made, and the variation diagrams 
constructed from them support the view that each of the series was 
evolved by a process of differentiation acting on a parent magma. 
From the composition of the amygdale minerals (which are referred 
to the closing phase of lava consolidation), it is deduced that the 
parent magma of the ‘alkali’ series was rich in carbon dioxide, and 
undersaturated in silica; whereas that of the ‘ calc-alkali’ series was 
rich in water and oversaturated in silica. The radio-activity of the 
lavas indicates that the depth from which the parent magma came 
was probably between 33 and 44 miles from the earth’s surface. The 
boundary fault along which the lavas are aligned seems to mark 
a zone where pressure was relieved to an extent and depth sufficient 
to promote fusion. 
