496 J. Allan Thomson—Inclusions in Volcanic Rocks. 
calcined, but when silicates are developed they are almost always 
wollastonite, augite, and garnet.1 The phenomena exhibited by the 
inclusions of the Portrush rock are then in complete conformity with 
the phenomena described by Lacroix. 
B. Homa@ogenovus [nctustons oF THE Coarse DoLERitE. 
These are rounded nodules about an inch and a half in diameter, 
and can be seen microscopically to consist of augite, felspar, and 
olivine. Microscopic examination shows that they are nolocrystalline 
with typical ophitic structure, the felspar being idiomorphic towards 
the olivine as well as towards the augite. The olivine percentage 
varies, and in the more basic types greatly exceeds that of the augite. 
The felspar is always abundant and consists of a basic labradorite. 
Magnetite is the only common accessory. It occurs in one slide in 
large idiomorphie crystals. 
These inclusions do not differ either in mineral composition or in 
structure from the rocks that enclose them, but they are still more 
coarsely grained. ‘They are normal ophitic dolerites. They probably 
represent secretions of the magma at a slightly greater depth, but 
under almost the same conditions of cooling as the sill. 
Professor Cole makes an interesting suggestion with regard to the 
possibilities of modification of the main mass of the dolerite. While 
he has identified andesine as the felspar, along the east shore the 
felspar seems to be always labradorite or anorthite. Clearly, as he 
says, ‘‘there is room for further research in this well-visited and 
attractive field.” 
II. Inclusions of the Kakanui ‘Mineral Breccia.’ 
This rock occurs on the sea-coast near the township of Kakanui, 
Otago, New Zealand. Its general characters and position in the 
stratified series have been described in a former paper.* It is a 
calcareous stratified breccia of Oligocene age, and contains a remark- 
able variety of crystalline volcanic products, as has already been noted 
by Mantell. There is no massive rock in the district that can be 
directly connected with it, although basaltic puys are abundant in the 
district, but it contains a few blocks of basaltic rocks which may be 
assumed to represent the lava-form of the magma by the explosion of 
which the breccia was formed. Enallogenous inclusions of gneiss, mica- 
schists, grauwacke, and limestones are not rare, but have not been 
studied. he chief interest lies in the size and the variety of the 
minerals, causing a great resemblance to the tuff necks of the Fife 
coast and to the diamond pipes of Kimberley, and in the nature of the 
homceogenous inclusions. 
The basaltic fragments are not fresh enough to ensure a good 
determination of the rock, but the two types may be recognised. Both 
contain pseudomorphs of red rimmed serpentine after phenocrysts of 
1 «« Tes Enclaves des Roches volcaniques,’’ p. 144. 
2 J. A. Thomson, ‘‘The Gem Grayels of Kakanui’?: Trans. New Zealand 
Institute, vol. xxxvili (1905), p. 481. 
3 Q.J.G.S., vol. vi (1850), p. 324. 
