OUTLINE OF THE GEOLOGY OF THE MOROBE GOLDFIELDS. 55 
on account of the geographical interval. For most practical purposes all 
the late porphyries and the volcanic activity can be considered together 
as one intrusive epoch. 
OTIBANDA SERIES. 
After the volcanic outbursts had largely expended their violence 
the Bulolo-Watut valley area settled down as a more restricted lake 
system, the limit of which was apparently about the present 3,800-foot 
contour. In this lake the Otibanda freshwater series of shales, mud- 
stones, sandstones and conglomerates was laid down, several hundred 
feet in thickness in the central portion, and intercalated near the base 
with bands of tuff and fine agglomerate representing the last phases of the 
dying volcanic activity. In these sedimentaries are found the first 
definite evidence of geological age on the Morobe Goldfield, apart from the 
Tertiary Langimar series to the west outside the true gold-bearing area. 
Bones of Nototheriam were collected from shale and sandstone beds at 
Otibanda, Upper Watut River, and these were identified by Dr. Charles 
Anderson (1) of the Australian Museum as similar to those obtained 
from Pleistocene and recent swamps of South Australia, though certain 
peculiar features of the jawbone suggested that they might be an earlier 
type. Numerous plant remains are also present in the series, but it has 
not been possible to make any age determination from them. The occur- 
rence of No'totherium, together with the recent aspect of the Otibanda 
series, is sufficient to establish this as Pleistocene, so that the principal 
volcanic activity, the later phases of which are interbedded in the Otibanda 
series, could not have taken place much earlier than the beginning of the 
Pleistocene. This means that the later porphyries belong to this period 
also, as porphyry exactly similar in type to the main late porphyry of 
the Upper Edie is found intruding the volcanic breccias in the Golden 
Ridges area. The injection of the late porphyries may, of course, have 
begun some time before this, but good grounds exist for considering that 
the whole of this period of activity belongs to Pliocene — early Pleistocene 
times. The Lower Edie type porphyry is much earlier, but there are 
no definite data on which to establish its age. 
RECENT DEPOSITS. 
Deposition of the Otibanda series appears to have been terminated 
by earth movements which initiated the drainage of the lake and slightly 
tilted the freshwater beds, a tilting which has been assisted by faulting. 
A great rush of detrital material from the slopes of Mount Kaindi 
followed the removal of the lake waters and formed piedmont deposits 
over much of the south-western side of the Bulolo Valley near Wau. 
The youngest rocks in the area, apart from recent stream gravels and 
terraces, are a limited series of rhyolite flows and rhyolite breccias on 
the surface of the piedmont deposits between Wau and Golden Ridges 
(Plate 2). 
GEOLOGICAL HISTORY. 
The chronological sequence in the Morobe goldfields area, as far 
as at present worked out, is set out in Table 1. Geological events which 
have taken place elsewhere on the mainland of the Mandated Territory 
