Alfred Harker—Rocks of the “ Beagle”? Collection. 108 
extinction-angles. There is an interstitial base of brown glass, 
Notwithstanding the presence of some felspar, the affinities of this 
rock are decidedly with the limburgites rather than the basalts. 
The caleareous deposit calls for no remark. The white balls, 
mostly from one to two inches in diameter, built up by ‘ Nullipore,’ 
are interesting as the analogue, on a giant scale, of a certain type of 
oolite. The alteration in the upper part of the calcareous deposit, 
where it is overlain by the younger lavas (‘‘ Volcanic Islands,” pp. 5, 6), 
is probably due to solution and recrystallization at least as much as to 
metamorphism. Darwin’s explanation of the curious intermingling of 
carbonate of lime and lava here, and again at Red Hill (pp. 10-14), 
will scarcely be accepted at the present day. He believed ‘‘ that the 
lime has been erupted, mingled with the molten lava.” Huis specimens 
seem to show merely a breccia of pieces of dark lava in a calcareous 
matrix, and again calcite and aragonite crystallized in the vesicles and 
interstices of a scoriaceous lava. ‘This is also the opinion which 
Doelter formed on the spot. 
The lavas which overlie the calcareous rocks of the coast district 
(pp. 9, 10) are, judging by the specimens, poorer in conspicuous 
phenocrysts than the lower lavas. Usually some small olivines are 
the only element visible to the naked eye. ‘The compact ground-mass 
has not the uniformly dark colour of the lower lavas, but is often 
mottled or streaked with lighter and darker shades of grey. A thin 
slice of one exampie [4703] shows small crystals of the usual olivine, 
pale augite, and magnetite, the olivine being largely replaced by 
pseudomorphs of a deep red-brown colour. In addition, there are 
small crystals of felspar with twin lamellation and low extinction- 
angles. There is finally an abundant isotropic base, quite colourless, 
enclosing very numerous slender needles of apatite. ‘This colourless 
base is partly segregated into little patches and streaks relatively free 
from the crystallized constituents (except apatite), and in these places 
it shows unmistakably the cubic cleavage characteristic of analcime. 
The rock may therefore be styled an analcime-basalt, allied to 
monchiquite, the presence of some felspar being the only character 
distinguishing it from typical monchiquites. 
In speaking of the lower lavas, the nature of the colourless isotropic 
base in the second and third types was left in doubt, its strictly 
interstitial occurrence making its identification a matter of difficulty. 
In the rock now considered, although isolation and chemical analysis 
are desirable to give confirmatory evidence, there can be no. reasonable 
hesitation in recognizing the colourless substance as analcime; nor is 
there any reason to question its status as a primary constituent of the 
lava. How fara like interpretation may be applicable to ‘limburgites ’ 
and ‘augitites’ with colourless base in the Cape Verd Isles and 
elsewhere, it would be rash to venture an opinion. If the colourless 
base in the rocks described above can be regarded as analcime, then 
[4705] may be named a monchiquite, and [4706] a monchiquite 
without olivine, or, according to the distinction made by J. F. 
Williams, a fourchite. 
The lavas of Signal Post Hill! (‘‘ Voleanie Islands,” p. 15) are 
1 ¢ Flagstaff Hill’ in Catalogue; ‘ Mte. Facho’ according to Doelter. 
