30 REPORT—1850. 
at intervals wholly irregular, but that in the intervals between (and preceding 
and following) these, there is occasionally a more or less continuous recur- 
rence of smaller shocks; these also have their irregular periods of greater and 
of less repose; so that‘on the whole the earthquake is often, as to time, likean 
occasional cannonade during a continuous but irregular rattle of musketry. 
The small rapid shocks are usually in close precession and succession to 
the great ones, and coexist with them. Thus, Don Palaccio Faxar, in his de- 
scription of the earthquake at Caraccas, of March 26, 1812, says, “ The 
weather being fine, a hollow roar like that of a cannon was heard and was 
followed by the shock, which lasted about 17 seconds; this was succeeded 
by a shock lasting 20 seconds; and after 14 seconds’ interval by a third of 
15 seconds’ duration. Total duration|1 minute and 15 seconds with a motion 
from W. to E.” (Quart. Journ. vol. ii. p. 402.) 
The total duration of motion (7. 6. of violent rising and transverse undula- 
tion) of the great earthquake of Caraccas (March 26, 1812), was estimated 
by some at 50 seconds, by others at 1 minute 12 seconds.—Humboldt, Per. 
Nar. vol. iv. p. 17. : 
Again, as to the New Zealand earthquake of 19th October 1848, “ At five 
in the morning a sharp shock. The extreme force of the shock lasted rather 
less than a minute; there was considerable motion for 34 minutes, and the vi- 
bration lasted for 8 minutes from the commencement of the shock.”— West. 
Rev. July 1849. 
The Syrian earthquake of 1759 also lasted altogether about 8 minutes 
(Dr. Russell, Phil. Trans. 1760), but a continuance of very small shocks at 
intervals, or of very small and rapidly recurring shocks, has been often ob- 
served for long periods of time. Thus, in the Andes, the earth has quaked 
incessantly for days together; and on the eastern slopes of the Alps of 
Mont Cenis, about Fenestrella and Pignerol in 1808, in North America, at 
New Madrid and Little Prairie, north of Cincinnati after 1811, and at Aleppo 
in 1822, shocks were felt hour by hour for several months ; so also at Comrie 
in Scotland, at longer intervals, they have long been felt ; and at Zante, in the 
Greek Archipelago, slight shocks, at all hours, are almost continual, as long as 
the present inhabitants recollect. 
Humboldt is of opinion that this prolonged continuance of slight shocks 
only occurs in districts remote from any active voleano. This however does 
not appear to be borne out by the observations made in New Zealand. In 
the earthquake there of October 1848, the shocks continued nearly five weeks 
before they became insensible, the district being one immediately adjacent to 
active volcanoes. There were during the larger portion of the time at least 
one thousand shocks per day. (West. Rev. July 1849.) 
The recurrence of slight shocks at nearly regular intervals, and having an 
apparent connection with the recurrent projections from closely adjacent vol- 
canoes, has been observed ; thus, Humboldt remarked shocks on Vesuvius and 
on Pichincha, which were regularly periodic, and from 20 to 30 seconds be- 
fore each projection of ashes and vapour. 
14th. The absolute area convulsed at one earthquake epoch, 
varies within indeterminate limits, and is related apparently 
in its extent to the maximum force of the shocks. 
Instances are recorded of very violent single shocks having been felt which 
were limited to very small areas, and here usually the direction of the shock 
has been nearly vertically upwards. This has been most remarkable in ob- 
servations made at sea; and slight shocks, however numerous, do not appear 
to actuate large areas, but in the greater earthquakes the total space shaken 
