Identifier: quarterlyjournal721916ge (find matches)
Title: The Quarterly journal of the Geological Society of London
Year: 1845 (1840s)
Authors: Geological Society of London
Subjects: Geology
Publisher: London (etc.)
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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apo River—2 miles north-west ofMochelia—a narrow dyke of hornblende-andesite penetrates a sheetof amygdaloid (H.A. in fig. 1, p. 226), and Mr. Wayland foundpebbles of pyroxene-andesite on the debris-strewn flats of the samedistrict. Here also fragments of tephritic pumice are found,though again not in situ. This rock clearly indicates another lineof variation which is more strongly represented in the north, forthe late Mr. R. L. Reid discovered an interesting occurrence ofphonolite associated with basalt and picrite-basalt in the neigh-bourhood of the Sanhuti River. Other rocks not found in situare solvsbergite and segirine-trachyte. Thus, there occur together,within the limits of what is a comparatively small volcanic field,lavas of both alkali and calc-alkali types. VI. Period op Eruption. The period of eruption of the amygdaloids cannot be definitelyascertained, but three lines of evidence point to their Tertiary,and almost certainly post-Oligocene, age. Q. J. Gr. S. No. 287. s
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(«) Eviden e from Faulting. In the district north of Mo-kambo Bay, between the Monapoand Mitikiti Rivers, sheets ofamygdaloid are seen to lie succes-sively on a surface of Cretaceoussandstones and limestones, andon far older crystalline rocks. AtMitikitis Kraal, only occasionalpebbles of agate and jasper re-main to prove the former extensionof the flows. The junctions be-tween sandstone and limestoneand between limestone and gneissare faulted, and it is evident thatdenudation kept pace with themovement and reduced the variousformations to a nearly plane sur-face before volcanic activity com-menced. Unfortunately, it is noteasy to determine the period offaulting. The Oligocene depositsof Lumbo, on the southern shoreof Mosuril Bay, are probablyfaulted down against the Creta-ceous sandstone, but the move-ment there may not have beensimultaneous with that within theCretaceous sediments, nor withthat between the latter and thePre-Cambrian complex. If it beconceded that all the faulting is

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