O94 PROCEEDINGS OF THE ROYAL SOCIETY OF QUEENSLAND. 
(3) Continuous tremors and microtremors, most of 
which are not felt. 
(1) In the first class must be placed violent earth- 
quakes such as shook the district in January, 1916. It was 
felt all over New Ireland and recorded in Sydney. <A house 
was thrown over as far away as Toma to the west. It was 
accompanied by a tidal wave of considerable dimensions. 
A steamer of about 2,000 tons, lying at the wharf at Rabaul, 
was at one moment above the sheds and shortly afterwards 
was bumped on the bottom of the harbour. The wharf 
itself, which was specially built to withstand earthquakes, 
was buckled up as if it had been crushed. The intensity 
and amplitude were so great that coconut palms were 
swayed to the ground and troops camped on Matupit Island 
became sea-sick. The narrow causeway which had until 
then joined Matupit Island to the mainland and formed 
a roadway sank several feet, cutting off communication 
except by boat. The stores in Rabaul suffered considerably. 
All their goods were thrown into confused heaps on the 
floor. Many of those who did not escape out of the bunga- 
lows quickly had exciting experiences with heavy articles of 
furniture which were thrown in all directions. 
Some wider tectonic origin must be sought for this 
class of shock. It is perhaps to be found in the readjusting 
and settling movements which must be frequently taking 
place in this somewhai unstable area. 
(2) The second class of shock consists of quakes of 
medium amplitude and less intensity than the former, and 
only affecting the vicinity of the craters. Some of these 
are sufficiently energetic to cause people to leave the bunga- 
lows or, if happening at night, to throw them out of bed. 
One of the more intense of these shocks occurred on 
Tuesday, 22nd May, 1917. It was felt at Kokopo, about 
twelve miles away, but not in the Duke of York Islands or 
New Ireland. It was preceded for some days by tremors 
and swarms of tremors with growing frequeney and 
intensity. Immediately preceding the shock the movements 
ceased, at least visibly, for about thirty-six hours. This 
space of quietness was followed, abont 9 a.m. on Tuesday, 
22nd, by three violent shocks lasting upwards of a minute 
eaen. Each shock was preceded by Icud rumblings, coming 
from the direction of the erater, becoming louder as the 
