Origin of the Pillow-Lava near Port Isaac. 577 
thickness. The pillows measure usually from 2 to 5 feet in 
diameter, but range up to 8 feet ; masses under 1 foot are rare. The 
individual pillows arc quite disconnected, although moulded on one 
another and adherent where they touch. Where three pillows 
approached there was an angular vacant space, subsequently filled 
with calcite, which is often altered into chert. Their mutual 
relations seem to prove that they were soft when deposited, but 
not sufficiently soft to squeeze into corners. 
Each pillow shows internally a central vacant space or very open 
sponge, often as much as 2 feet in length. This is succeeded by a 
thick shell of exceptionally vesicular lava, which is followed by an 
outer shell of banded, more or less vesicular rock. The whole mass 
is so vesicular that it must have been very light. 
If this lava were subaerial, the lightness would not help us to 
explain the origin of the isolated pillows ; but the intimate asso- 
ciation with fine-grained marine strata shows that it was probably 
submarine. On calculating the proportion of cavity to rock in two 
of the pillows, the authors find that the specific gravity of the whole 
mass must have been very low, not greatly exceeding that of sea- 
water. The lava seems to have been blown out into thick-walled 
bubbles, kept from touching each other by the escaping steam. The 
whole mass was for a short time in the spheroidal state, and, 
although composed of a multitude of large plastic spheres, the sheet 
could flow like a liquid. This eruption seems to have been analogous 
to that of Mont Pele, described by Dr. Tempest Anderson & Dr. Flett, 
except that it was submarine instead of subaerial. 
2. 'On the Subdivision of the Chalk at Trimmingham (Norfolk)/ 
By Reginald Marr Brydone, F.G.S. 
The object of this communication is to lay before the Society a 
sketch-map showing the geographical distribution of the sub- 
divisions, with a brief account of their distinguishing features. 
Practically the whole of the Chalk exposed on the foreshore comes 
under two main divisions — one composed of (a) Sponge-beds, very 
largely yellow, 12 feet, resting on 8 feet of White Chalk ; (b) White 
Chalk without Ostrea lunata, about 9 feet thick ; (c) White Chalk 
containing 0. lunata, 20 feet ; and the other composed of (a) Grey 
Chalk, about 12 feet thick; succeeded by (b) White Chalk with 
Ostrea lunata, about 20 feet ; (c) White Chalk without 0. lunata, 
about 8 feet; (d) White Chalk with 0. lunata, about. 10 feet; and 
(e) Grey Chalk, about 25 feet. There is no evidence as to the 
relative positions of these two main divisions. The author seeks 
to justify his adoption of Terebratulina gracilis and T. Gisei as the 
zone-fossils of the Trimmingham Chalk, in opposition to the proposal 
to adopt Ostrea lunata as the zone-fossil. Other important species 
are Pentacrinus Agassizi, P. Bronni, and Echinoconus Orbignyanus. 
The author still adheres to his view that these masses of Chalk 
