94 REPORT—1858. 
The vertical component of motion has only been given in one instance 
here ; but there is every reason to presume that the angle of emergence of 
the seismic wave all over the northern continent of America is steep. 
TasLe XVI.—Earthquakes of Mexico and Central America. 
Earthquakes with date of Day or Month. % 
@ = 
Century. : 5 B |e 3 S| Total. 
a@|/s/e]- ; seb es gH] Daal Cae FI 8 iso 
Ss = = a o a Pe) [a Q o pe 
elelial/R|Si18/S| FP] 2/815] 8 = 
ei eee 4S SS srt a | SO Nae ney 
GVA Wee oo Pipe oa tate can PCC “Bs ifs |Seeeo|! aly Poem 6 
SANE aes he fone Ga ie oa Pre] Wee el tees al fee ear 7 
XVIII oe ot eal ee Seley! AE aed nome tae ORO ||| 224 
XIX. Bl Bel De DE Gus ee, sie ads NT esis onal eres ta em an aD 
Total 3/5} 8B) S48) Fy) Al 2) Ay 4 Salm tebe 
Winter Spring Summer Autumn 
16 16 10 10 
The steep emergence of the wave is most remarkable in Mexico, whiere, at 
Acapulco, it is frequently felt as a directly vertical pulse from beneath (as 
at Riobamba). 
Perrey does not attempt, from his materials, a full discussion of the hori- 
zontal component of motion. The prevailing impression in Mexico is that 
the direction of shock is parallel to the chain of the Cordilleras. Some, how- 
ever, of the most remarkable shocks have apparently moved at right angles 
to the preceding. 
The truth is, in a wide region situated close to, and no doubt in great part 
close above, vast centres of disturbance, whose pulses reach the surface gene- 
rally with large angles to the horizon, there must be horizontal components 
in every azimuth, and only distinguishable in one more than another, as the 
accidents of the originating blows, of the heterogeneous formations through 
which they are transmitted, and the opportunities of exactness of obserya- 
tion, &c. vary. 
Perrey concludes this memoir with a résumé of the labours of Arago, Von 
Buch and Berghaus, on the voleanoes of Mexico and the Andes. 
In his memoir on the Antilles, Perrey includes Cuba, which has also been 
the subject of research to M. Poey, now stationed at the Observatory of 
Havanna—with Hispaniola, Jamaica and Porto Rico in the greater, and in 
the lesser isles Antigua, Barbadoes, St. Christopher’s, Guadaloupe, Mar- 
tinique, Granada, Trinidad, St. Thomas, Santa Cruz, Dominica, St. Vin- 
cent, Tobago, and St. Lucia, &c. In discussing the copious materials at his 
disposal in this vast region, Perrey has found it necessary to adopt certain 
conventional licences with reference to some of the very prolonged earth- 
quakes, whose slight but continuous shocks have often (as at Comrie and 
East Haddam) lasted for a great length of time, reckoning each month of 
such shocks as equivalent to one great earthquake. 
In the following table, XVII., he has given the distribution in time :— 
