Royal Society. : 149 
mosphere. The author is disposed to place but little reliance on most 
of the supposed prognostics of these convulsions: but he mentions 
that, previously to the earthquake described in the present paper, there 
were seen immense flocks of sea birds, proceeding from the cuast to- 
wards the Cordillera, and that a similar migration had been noticed 
prior to the great shock of 1822. From his own observations, he con- 
cludes that the barometer usually falls shortly before any considerable 
shock, and that it afterwards rises to its ordinary mean height. Both 
before, and also at the time of the convulsion, the volcanos of the 
whole range of the Cordillera were observed to bein a state of extra- 
ordinary activity. 
The earthquake began at half-past eleven o’clock in the morning 
of the 20th of February. The first oscillations of the earth were gen- 
tle, and attended with little noise : they were succeeded by two ex- 
tremely violent tremors, continuing for two minutes and a half, the 
principal direction of the motion being from south-west to north-east ; 
and they were attended by aloud report, apparently proceeding from 
the explosions of a volcano to the southward. All the buildings of 
the town of Conception were thrown down during these undulations. 
At the expiration of half an hour, when the inhabitants, who, on the 
first alarm, had fled to the neighbouring heights, were preparing to 
return to their houses, it was observed that the sea had retreated to 
such a distance that the ships in the harbour were left dry, and all 
the rocks and shoals in the bay were exposed to view. At this pe- 
riod an immense wave was seen slowly advancing towards the shore, 
and, rolling majestically onwards, in ten minutes reached the city of 
Conception, which was soon overwhelmed in a fiood of an altitude of 
28 feet above high-water mark. The few persons who had remained 
in the town had but just time to make their escape, and to behold from 
the rising grounds, the complete submersion of the city. All objects 
that were movable were swept away into the ocean by the reflux of 
this great wave, which was succeeded by several similar, but smaller 
waves, completing the work of destruction, and leaving behind them, 
on their final retreat, a scene of universal havoc and desolation. 
The island of Santa Maria, which is situate to the southward of the 
bay of Conception, and is about seven miles broad, and two long, re- 
mained, after the earthquake, permanently elevated at least ten feet 
above its former position; anda similar change was found to have 
taken place with regard to the bottom of the sea immediately sur- 
rounding the island. The amount of this elevation was very accurately 
ascertained by the observations of Capt. Fitzroy, who had, previous] 
to the earthquake, made a careful survey of the shores of that island ; 
thus supplying the most satisfactory and authentic testimony to this 
important fact. 
‘The author gives, in the course of the paper, several particulars re- 
lating to the effects of the earthquake in different parts of the Chilian 
coast; the oscillations appearing to have extended to the north as far 
as Coquimbo, and to the east as far as Mendoza, at the ridge of the 
great chain of the Andes. Vessels navigating the Pacific Ocean, 
within a hundred miles of the coast, experienced the shock with con- 
siderable force. Its influence was very perceptible in the island of 
