Geological Society of London. O29 
This basalt-glass is frequently traversed by numerous joints; it is 
occasionally finely columnar, and sometimes perlitic in structure. 
From the acid glasses (obsidian) it is distinguished by its density, 
its opacity, its magnetic properties, and especially by its easy fusibility, 
from which the name of tachylyte is derived. By its greater hardness 
it‘is readily distinguished from its hydrated forms (palagonite, etc.). 
In its microscopic characters basalt-glass is found to resemble other 
vitreous rocks; thus it exhibits the porphyritic, the banded and fluidal, 
the spherulitic, and the perlitic structures. In the gradual transition 
of this rock into basalt, all the stages of devitrification can be well 
studied. 
The difference between these locally developed basalt-glasses and 
the similar materials forming whole lava-streams in the Sandwich 
Islands was pointed out in the paper, and the causes of this difference 
were discussed. 
It was argued that the distinction between tachylyte and hyalome- 
lane, founded on their respective behaviour when treated with acids, 
must be abandoned, and that these substances must be classed as rocks 
and not as mineral species; the name basalt-glass was adopted as best 
expressing their relations to ordinary basalt, the term tachylyte being 
applied to all glasses of basic composition and being used in contra- 
distinction to obsidian. 
2. “On a Section recently exposed in Baron Hill Park, near — 
Beaumaris.”” By Prof. T. G. Bonney, M.A., F.R.S., Sec. G.S. 
The author, about three years since, observed some imperfect ex- 
posures of a felsitic grit in the immediate vicinity of the normal 
schists of the district in a road which leads from Beaumaris cemetery 
to Llandegfan; but last summer had the opportunity, through the 
courtesy of Sir R. B. Williams, of examining the cuttings made in 
constructing a new drive, which runs through Baron Hill Park very 
near the above outcrops. After tracing the normal schists along 
the steep scarp of the hill, he came, after an interval of about 60 
yards, covered by soil and vegetation, to a massive grey grit con- 
sisting of quartz, felspar, and minute fragments of compact felsite, 
which now and then attain a larger size, being an inch or so across. 
These grits, which pass occasionally into hard compact mudstones 
(probably more or less of volcanic origin), can be traced for some 
350 yards to the neighbourhood of the above-mentioned road, which is 
crossed by a bridge; and a short distance on the other side of this 
is a considerable outcrop of the grit, which in places becomes coarsely 
conglomeratic, containing large fragments of the reddish quartz-felsite 
so common on the other side of the straits in the beds at or below the 
base of the Cambrian series. The schists appear to dip about 20° 
H.S.E., the grits about 25° HK. 
The author, after describing the microscopic structure of the various 
rocks noticed, pointed out that this section, though the junction of the 
two rocks is probably a faulted one, has an important bearing on the 
question of the age of the Anglesey schists, micaceous and chloritic. 
The Survey regards them as altered Cambrian; it has even been sug- 
gested that they may be of Bala age; others have regarded them as 
Pebidian. Now the felsitic grits and conglomerates cannot be newer 
