MICROSCOPICAL INVESTIGATION. 549 
Zealand; its circumference—exclusive of its numerous bays—is about 
88 miles. Full information regarding the geological structure of the 
Peninsula and the macroscopic characters of some of iis rovks are 
contained in Dr. von Haast’s Geology of the Provinces of Canterbury 
and Westland. A short summary is also to be found in the 
geological description of New Zealand by Hochstetter. 
From these researches and from-the geological map appended to 
Haast’s work we learn that Banks’ Peninsula represents a small, 
isolated volcanic territory in which several craters of extinct volcanoes 
are still preserved in recognizable form. Old crater-walls surround 
deeply-cut depressions—Calderas—into which steep-walled entrances 
—Barrancas—lead. Four craters with their approximate limits are 
marked on Haast’s geological map. They open seawards and give 
rise to the formation of huge bays. 
The Peninsula,—exclusive of a narrow zone of palceozoic strata 
situated near Lyttelton harbour—consists entirely of volcanic rocks. 
Systems of lava-streams which alternate with tuffs and agglomerates, 
form the walls of the calderas, and these have a regular slope out- 
wards from the centre of the depressions. Similar volcanic rocks 
compose the higher mountains, and their lavas have flowed into the 
previously formed calderas. The last and weakest eruptions now 
represent small islands or peninsulas near the centre of the deeper 
depressions. According to Haast, the oldest tertiary minerals are 
finely-laminated rhyolites showing prismatic structure and changing 
at the margins into greenish or brownish obsidians. Then follow 
streams of basaltic lava with beautiful prismatic structure. Lastly 
come rocks, also called basalts by Haast, in which thick and compact 
varieties change into anamesites and dolerites, as well as into scoria. 
With one exception the streams consist of basic materials, and the 
dykes are mostly trachytic. The latter have in many cases altered the 
neighbouring agglomerates and tuffs into tachylyte-like substances, 
while the basaltic rocks have produced no such alterations. The 
dykes radiate from the centre of the eruption. 
The best section is given by the oldest crater, opened by a railway 
tunnel, and called Lyttelton Harbour caldera; this has an average 
diameter of two miles. ‘The grain of the lavas varies between that of 
the dolorites. and dense basalts. The centre of very large lava 
streams often consists of compact black basalts with a few large 
crystals, while towards the surface the colouration becomes lighter 
and the structure more porphyritic and scoriaceous or amygdaloidal. 
In the same way also the structure and colour change within each 
stream with the distance from the point of eruption; compact black 
basalts change by degrees into greyish-coloured dolerites, and there 
appear numerous crystals of augite, basaltic hornblende, rubellane, 
and more especially labradorite. Haast particularly refers to the 
rare occurrence of olivine. Of secondary products there are enumerated 
spherosiderite, calcite, arragonite, chalcedony, jasper, opal, hyalite, 
natrolite and iron-pyrites. 
Apart from the clastic minerals—more especially a great variety 
of basaltic tuffs and agglomerates—there are to be found in the 
collection of orthoclase rocks which I have examined, liparites and 
trachytes ; in the plagioclase rocks, augite-andesites and basalts. In 
