66 
Proceedings of the Royal Society 
of some of tlie more typical necks or volcanic funnels which sup- 
plied the sheets of rock now so abundant at the surface, and com- 
parisons are drawn between their characters and those of tertiary 
and recent cones and craters. The numerous intrusive sheets and 
dykes are described in their relation to the surrounding rocks and 
to the position of the volcanic vents. An account is given of the 
bedded lavas and tuffs so copiously interstratified with the Carboni- 
ferous formations, and their identity with modern volcanic masses 
is insisted on. 
The second part of the paper deals with the petrography of the 
igneous rocks, and more especially with their characters as revealed 
by the microscope. The author states that he has been engaged 
during the last ten years in carrying on this investigation, and that 
he has studied some hundreds of slices of the rocks from all parts 
of the region. After alluding to what has been published by other 
observers on this subject, he proceeds to describe the rocks under 
the two main divisions of, I. Crystalline ; II. Fragmental. 
I. Crystalline. — These embrace all the melted or lavaform 
rocks. They may be subdivided into four classes : — 1st, Augite- 
Felspar Rocks, which include three types of structure — (1) granitoid, 
consisting of a crystalline mixture of a triclinic felspar (but some- 
times orthoclase), augite, titaniferous iron, and apatite, with occasion- 
ally biotite, and more rarely quartz ; (2) Doleritic — a crystalline 
mixture of triclinic felspar and augite, with titaniferous iron or 
magnetite, apatite, and frequently olivine, with a variable propor- 
tion of a half-glassy ground-mass ; (3) Basaltic — a mixture of 
minutely granulated (and larger, more definitely crystallised) augite, 
triclinic felspar, magnetite, and olivine, with usually some apatite 
in a glassy or half-glassy ground mass. 2d. Olivine ( Serpentine ) 
Augite Rocks, consisting mainly of serpentine throughout, while 
abundant crystals of altered olivine occur, fresh augite, titaniferous 
or magnetic iron, apatite, and occasionally traces of a triclinic 
felspar. Where the last-named mineral increases in amount, the 
rock assumes the character of a much altered “diabase.” 3d. Fel- 
spar-magnetite Rocks , consisting essentially of a triclinic felspar and 
grains or shred-like particles of a black magnetic mineral, sometimes 
with large orthoclase crystals, rarely with augite, in a porphyry 
ground-mass. 4th. Orthoclase Rocks or Felsites. 
