4 
PACIFIC SCIENCE, Vol. XII, January, 1958 
the island. The largest of the old volcanoes 
was probably in the position of the present 
Mt. Pagan. The uppermost unit of the suc- 
cession is composed of a widespread thick 
tuff-breccia sequence. 
The pre-caldera group is probably of late 
Quaternary age. Sea cliffs have been cut in the 
breccias and older deposits; and reef lime- 
stones, some of which are now as much as 5 
feet above present sea level, have since been 
deposited on the wave-cut platforms. Similar 
sea cliffs flanked by terraces and raised reef 
limestones have been noted on the coasts of 
many Pacific islands and are attributed to 
erosion and deposition during post-glacial 
high stands of sea level. Sea levels 5 to 12 
feet higher than the present one have been 
assigned various dates ranging from about 
1,000 to 5,000 years ago. Some plants that 
may have been introduced by man are rep- 
resented by impressions in samples collected 
from the upper breccias and therefore may 
indicate a maximum age for these breccias of 
about 4,000 years— the probable length of 
time since the advent of man in Micronesia 
(Spoehr, 1955^, 1955 b). 
The post-caldera succession is concentrated 
within the calderas. At some places lavas have 
flowed over the caldera rims; tuff as much as 
30 feet thick mantles large portions of the 
caldera blackslopes and the isthmus. 
Historic records of eruptions are scattered, 
conflicting, and incomplete. It is likely that 
several major eruptions have taken place 
within the past 200 to 300 years. Marche 
(1891: 261) states that a major eruption oc- 
curred in 1872. Extensive lavas northeast and 
southwest of Mt. Pagan and a thick tuff 
sequence to the west were probably deposited 
at this time. Eruptions since 1900 have been 
minor. 
VEGETATION 
The present-day vegetation of Pagan gives 
a general impression of semi-aridity. This is 
probably not so much a reflection of climatic 
dryness as of an extremely porous substratum 
and of the pioneer nature of vegetation, which 
occupies surfaces of recent volcanic ejecta. 
In the very few low, wet areas, such as to the 
west and southwest of the Inner Lake, 
thickets of broad-leafed trees are luxuriant 
enough, and places bordering the lake are 
somewhat marshy. Luxuriant patches of 
woods also exist in hanging valleys on the 
west side of the south end of the island. A 
mixed scrub forest of low stature forms 
thickets and patches up to several acres in 
extent on plains north and south of Mt. 
Pagan — extending up its lower slopes in 
places on steep slopes on the west shore of 
the isthmus, and in numerous ravines through- 
out the island. There has been no investiga- 
tion of the actual composition of this forest, 
but it contains 15 or more species of trees. 
The loose volcanic ash that covers large 
areas, especially on the west side, is largely 
vegetated by an almost pute stand of sword- 
grass, Miscanthus floridulus (Labill.) Warb. 
This forms a coarse, harsh, brake-like grass- 
land 1 to 3 m. tall and very dense in places. 
On the steepest slopes and above 250 m. 
altitude this grass tends to be shorter and 
the clumps more widely spaced. Above 450 
m. it is sparse to absent. 
Lava flows may be practically bare, as on 
the northeast side of Mt. Pagan; they may 
support scattered clumps of Miscanthus and 
trees of Casuarina , as on the east and south- 
east sides of Mt. Pagan and the central upland 
of the southern part of the island; or, as on 
many of the flows and lava cliffs to be seen 
along both sides of the island, they may be 
covered by almost pure forests of Casuarina . 
Casuarina and the fern, Nephrolepis hirsutula 
(Forst. f.) Presl, are among the earliest in- 
vaders on new lava. Both species were well 
established on a fresh black aa flow in the 
depression at the west base of Mt. Pagan in 
1950. This flow has been dated by Tanakadate 
(1940) as having occurred in 1925. It shows 
no visible weathering. 
On plains of ash soil the vegetation is gen- 
