Lower Silurian Lavas of Eycott Hill. By J.C. Ward. 243 
(12) Lava.—Lithological: purplish crystalline base, with many 
small porphyritically imbedded crystals. 
Microscopical: plagioclase crystals of various sizes imbedded in 
minutely crystalline base. Magnetite and chlorite, and many 
brownish-red specks of iron peroxide. Many of the larger crystals 
of felspar, besides having numerous reddish specks and _ lines 
scattered throughout them, are permeated by slender veins filled 
with chlorite. Portions of the base are also sometimes enclosed (or 
partially so) within the large crystals. No unaltered augite is dis- 
cernible, but in other respects the general crystalline appearance is 
quite that of the basaltic class of rocks. 
For a chemical analysis of this rock, see p. 246, No. 3. 
(13) Lava.—Lithological: compact dark-blue base. 
Microscopical: consists wholly of a minutely crystalline mixture 
of felspar needles, augite grains (a good deal altered), and mag- 
netite, together with chlorite. 
For a chemical analysis of this rock, see p. 246, No. 4. 
A thin band of ash and breccia parts this thick series of lavas 
just described from the following. 
(14) Lava.—A vesicular form; small vesicles in a compact 
greenish base. 
(15) Lava.—Lithological: grey-blue and highly crystalline 
base, slightly effervescing with acid. 
Microscopical: highly crystalline ; plagioclase crystals from the 
size of the ordinary needles up to those of + inch in length, show- 
ing the banded structure remarkably well. The larger crystals 
frequently enclose portions of the base. Magnetite, chlorite, and 
calcareous matter disseminated. 
For a chemical analysis of this rock, see p. 246, No. 5, 
(16) Lava.—Much the same as the last. 
(17) Lava.—Lithological: compact grey base, with small 
obscurely-defined crystals and wavy reticulated lines. 
Microscopically this is perhaps one of the most interesting 
rocks of the whole series. ‘The base is minutely crystalline, in- 
numerable small felspar needles all setting parallel to one another, 
and having a well-marked flow around larger and porphyritically 
imbedded crystals, much altered. Among the needles is much 
chloritic matter, and magnetite in fine grains. The crystalline flow 
is shown in plain light in Fig. 3, and under polarized light in 
Fig. 4. There are also certain darker bands, roughly parallel to 
one another, along which the chloritic matter seems to have been 
converted into a dark-brown or reddish product; these bands 
sometimes slightly cross the direction of flow. 
In the example shown in Fig. 3, the porphyritically imbedded 
plagioclase crystals often contain parts of the base enclosed within 
them, and portions of their outline are very indistinct, with 
