242 Transactions of the Royal Microscopical Society. 
(5) Ash (100 to 120 feet thick).—This bed serves as a good 
instance of the value of microscopic examination. It is of so 
fine-grained a texture that I had originally taken it to be one of 
the more compact lava-flows, and had no suspicion of its ashy 
character until examining it under the microscope together with 
the other rocks in the same series. Unlike most of the fine ash- 
beds it is free from bedding, and evidently consists of closely com- 
pacted fine volcanic dust. Microscopic examination shows that the 
fragments are pretty uniform in size, and that many consist of 
lava. 
Next above this ash comes a great thickness of lava-flows, 
between 700 and 800 feet. They are numbered on the section 
6 to 13. A little farther north than our line of section a band of 
ash and breccia occurs among these flows, but dies out southwards. 
(6) Lava.—Lithological: a very compact and dark base, with 
small felspar crystals. 
Microscopically the base is minutely crystalline, with small 
felspar needles, very small magnetite grains, and disseminated 
chloritic matter. Larger crystals of plagioclase felspar very much 
altered. Very little unaltered augite. Some pseudomorphs, ap- 
parently after olivine. ‘Small vesicles filled with calespar and 
chlorite. 
(7) Lava.—Lithological: compact greenish-grey base, with 
small felspar crystals and dark spots; breaking with conchoidal 
fracture. 
The microscopic structure of this bed is shown in Fig. 2, Plate 
CLXXXII. The base consists of the usual mesh-work of minute 
felspar prisms with chlorite and magnetite, and in it are larger 
imbedded crystals of felspar, all highly altered. There are many 
chloritic pseudomorphs, but no unaltered augite. 
(8) Lava.—tLithological: fine-grained base, with a reddish 
tinge, and containing small crystals and spots. 
Microscopical: a crystalline mixture of small felspar prisms and 
small grains and crystals of altered augite (?), with sparsely scattered 
magnetite. Some larger, but highly altered, felspar crystals, and 
many small vesicles filled with chlorite and calcite and haying a 
crystalline edging. 
(9) Lava—A compact form. 
(10) Lava.—Lithological: a compact greenish base, with 
small felspar crystals. 
Microscopical: fine crystalline base of felspar needles, mag- 
netite, and chloritic (altered augitic) matter, with porphyritically 
imbedded crystals of plagioclase felspar, and perhaps some ortho- 
clase pseudomorphs, after augite and olivine. 
(11) Lava.—-On the whole, similar to the preceding, but very 
vesicular. 
