314 Scientific Intelligence. 
Spain is the great number of minor shocks which usually follow, 
and which at times also precede the maximum shock of each 
seismic period; but in these seismic periods the position of the 
maximum shock of the period with respect to the others is not 
constant. In general the period opens with the maximum shock, 
yet with some preceding small shocks; then follow many minor 
shocks; then, after a few months, a second scismic period com- 
mences in the same area which begins with a shock that is even 
heavier than the maximum of the first period and is preceded 
sometimes also by small shocks. 
5. Considering the chronological distribution of earthquakes in 
a given region, or in the whole peninsula, no periodical return of 
the maxima is made out, neither decennial nor of any other 
period; but there is a certain approximately secular return, bisecu- 
lar or trisecular. 
6. As regards the seasons, the greater number of earthquakes 
in Spain occur in the autumn and winter, as compared with the 
summer and spring. 
The able discussion leads the authors to the following general 
conclusions : 
The great earthquake of 1884 shook an area not volcanic, but 
one that was in line with the perimeter of the Mediterranean 
basin, with the voleanic and seismic zone of Southern Italy, 
Greece, Asia Minor, ete.; and should be classified therefore with 
the perimetric earthquakes, of so frequent occurrence in Southern 
Italy. The seismic movement radiated from a center of ellipsoidal 
form, at a depth of 12 or 13 kilometers, and was thence propa- 
gated in the earth’s crust according to the fundamental laws of 
molecular movement in solids. The seismic wave was deviated 
by refraction, and especially by reflexion, in traversing rocks of 
different density and elasticity. 
The velocity of transmission could not be determined ; yet it 
is made evident that in all directions the rate was less than the 
propagation of sound in the earth’s crust. 
The seismic wave was propagated most easily and uniformly, 
and with relatively less destruction, in the compact crystalline 
rocks of the Archean and Paleozoic. The general direction of 
the bedding favors transmission of the seismic movement propa- 
gated parallel to it,and is an obstacle to movement in a transverse 
direction. 
The seismic movement in passing from the more compact and 
relatively elastic Archean and Paleozoic rocks to a region of 
marls, clays, travertine and the like is transformed into move- 
ment of mass, producing more disastrous effects the less the com- 
pactness, continuity and homogeneity of the superficial beds. 
The intensity of the Andalusian earthquakes of 1884 at the 
center was greater than that of the Neapolitan of 1857, the 
Ischian of 1883, ete.; but it reached the surface with less energy, 
producing less disastrous effects in proportion to the greater depth 
of the center and the greater width of the shaken area. Yet the 
