J. Allan Thomson—Inclusions in Volcanic Rocks. 499 
Under type C may be grouped all the stages from large erystals of 
brown hornblende, containing subsidiary inclusions of garnet and 
biotite, down to the types under B, where hornblende is an accessory 
mineral. 
Another rare type of rock in the breccia seemed to consist of 
kernels of altered olivine nodules cemented by hornblende and biotite. 
No material fresh enough for microscopic study could be obtained. 
The similarity of olivine nodules to lherzolites has long been 
known. Lacroix regards them as having been formed by segregation 
in depth in the basalt magma, forming a crust on the walls of the 
reservoir that has been broken through on eruption. Although their 
chemical composition is more basic than that of the basalt which 
encloses them, and the whole magma could not have crystallised out 
as lherzolite, yet a considerable mass of the rock might conceivably 
be formed. In a rock so little felspathic as the Kakanui basalt one is 
not surprised by their abundance, while the similarity of the other 
types to the basic rocks found in association with lherzolite is only 
what might be expected. It will be of interest to demonstrate this 
similarity. 
In his study of the basic rocks accompanying the lherzolites and 
ophites of the Pyrenees,’ Lacroix describes two series of rocks: the 
first, which he has named ariégites, always occur associated with the 
lherzolites; the second, various hornblende rocks, occur as veins in 
the lherzolite, or in separate bosses. Lherzolite is not always a 
homogeneous massive rock, but is often banded, at the Etang de Lherz 
for instance, one band being formed of normal lherzolite, the other of 
ariégite. It is distinguished from lherzolite by the absence of olivine 
and enstatite, and consists in the normal type of a monoclinic augite 
and abundant spinel, while subsidiary types are formed by the presence 
of garnet and basaltic hornblende. The structure is sometimes like 
that of lherzolite, sometimes kelyphitic. 
The inclusions grouped under A above will be readily seen to 
resemble in all respects lherzolites and ariégites. It should be 
remembered that the lherzolite at Lherz contains hornblende. 
Under the name of garnetiferous hornblende ariégite is described 
a rock consisting of brown hornblende, some flakes of mica, and large 
grains of red garnet with a little magnetite and spinel. The general 
resemblance of the types placed under C to this rock is sufficiently 
evident. 
The second series of rocks accompanying the lherzolite is very 
varied, but is characterised by the presence of brown basaltic horn- 
blende as an essential mineral. Among these rocks are hornblendites, 
pyroxene hornblendites, and hornblende peridotites. The extreme 
types of inclusion under C may be called hornblendites. 
In none of these Pyrenean rocks is there any augite that at all 
resembles that in the B type of inclusions. The extraordinary colour 
is probably due to a high percentage of titanium. The rocks do not 
probably differ much in chemical composition from garnetiferous 
ariégites. 
1 Comptes Rendus viii International Geological Congress, 1900, p. 806. 
