248 MR. H. H. AENOLD-BEMEOSE ON A SILL AND [May 1 899, 



darker spots scattered throughout, and coutain very thin veins, 

 strings, and patches of a greenish material which is grey in polarized 

 light. A few minute fragments of quartz or felspar are also present, 

 but are too small for testing in convergent light. 



{d) The Limestone below tlie Igneous Rocks. 



The limestone below the dolerite varies in character. In places 

 it is mainly composed of bunches of corals ; in others it is fine- 

 grained and laminated, and in yet others it appears to be an 

 aggregate of nodules. 



A specimen of the nodular limestone below the lava opposite the 

 quarry is a clastic rock made up of fragments of shells, encrinite- 

 stems, and other organisms, and also of irregularlj^-shaped pieces of 

 a dark, previously-consolidated limestone containing encrinite-stems. 

 A few small fragments of tuff are probably present in it. A similar 

 rock, partially indurated, is found beneath the clay. It is composed 

 of more or less rounded fragments of a very fine-grained brown 

 limestone without fossils, and of a limestone with shell-fragments 

 considerably altered, mingled with small patches or shreds of a 

 green material which are isotropic, and probably tuff-fragments. 

 The various portions are cemented by crystalline calcite. 



The laminated limestone 6 feet below the clay, which was taken 

 for a datum-line (see p. 243), contains foraijiinifera and a few shell- 

 fragments in a matrix consisting partly of finely-crystalline calcite, 

 and partly structureless. It is traversed by veins of iron-oxide. 

 The same bed, where marmorized, is composed entirely of crystalline 

 calcite in minute grains, with no traces of fossils. It is remarkably 

 free from impurities, and the laminae of which it is made up average 

 about -gL- inch in thickness. ... 



(e) The Tuff near the Northern Fault. 

 The tuff near the northern fault (see p. 245) consists of lapilliin a 

 cement of calcite. The majority of them are crystalline, and many 

 are vesicular. The crystalline fragments contain felspar, pseudo- 

 morphs of olivine, and probably of augite, in a groundmass, which is 

 sometim.es opaque with iron-oxide. The larger felspars are twinned, 

 and have a fairly sharp outline. The felspars in those fragments 

 which have a lighter-coloured groundmass are often skeleton-crystals 

 and microlites, and the lath-shaped sections frequently have jagged 

 ends passing into microlites. The rock is in a much fresher state of 

 preservation than that in which the bedded tufis of the district are 

 generally found, and is hard enough for an agglomerate. (PI. XX, 

 %. 6.) 



(/) The Lava-flows south of the Inlier. 



A specimen from the upper of the two lava-flows, south of the 

 inlier, consists of felspars in a base of iron-oxide ; they occur in 

 lath-shaped sections, in bundles and plumes of microlites, and in 

 skeleton-crystals. Pseudomorphs of olivine and possibly of augite 

 are present. (See PI. XX, fig. 5.) 



