On the so-called Spilites of Jersey. 61 
In the field it was hardly possible to fix the precise boundaries of 
the above varieties of ‘“‘spilite,” or to determine their dip, so that 
the order of succession is doubtful. 
Small quarries have been opened to the north of the pit just 
described. In most of them little could be seen, but one, some 50 
yards to northward of the last-named, gave the section as figured 
and showed the “spilites” to be the result of contemperaneous 
volcanic action. 
(1) ‘* Spilite,’’ somewhat porphyritic. 
(2) ‘‘Spilite,’’ rather amygdaloidal. 
(3) Well banded green argillite and fine grit, dipping roughly at about 45° to 
W.S.W. and passing down into. 
(4) A breccia, the fragments being a compact purplish “ spilite,’’ sometimes 
amygdaloidal, rarely porphyritic, the matrix rather rotten. The breccia is 
exposed for about five feet vertical. 
A comparison of the rocks exposed in these openings made it 
probable that (4) is underlain by another mass of “ spilite,” i.e. that 
two lava flows are parted by a breccia and a little banded gritty 
argillite. 
Slides have been examined of three typical specimens obtained 
from the large quarry. In all of them the most important con- 
stituent of the compact ground mass is felspar in small crystals, 
generally lath-shaped, with a small extinction angle, apparently 
oligoclase. These microliths are separated by an aggregate material 
which appears in some cases to result from the alteration of the 
augite in a microcrystalline or micro-ophitic ground-mass. In no 
slide can the remains of original glass be identified with certainty, 
but a flow structure is not infrequently exhibited by the matrix in 
an orientation of the felspar microliths. In one slide some of the 
large broad porphyritic felspars (completely replaced) have a form 
rather like that of orthoclase, and in another slide a few examples 
resemble sanidine. But in the best preserved crystals the twinning 
is generally on the albite plan, the form is sometimes elongate, and 
the extinction often is at a low angle. Thus it seems that the 
majority are plagioclase. Other crystals are completely replaced, 
generally by viridite or chlorite, but have retained a definite form 
and appear to represent a ferro-magnesian silicate. Iron oxide is also 
present sometimes in the form of ilmenite. Amygdules, especially in 
one rock, are fairly large and numerous. The minerals of secondary 
origin in the slides include viridite, a chlorite (sometimes apparently 
