379 
THE MEDITERRANEAN NATURALIST 
ting nature The number of microbes of all kinds 
was found to average 761,521,000 per gram, or 
about 21,600,000,000 per avoirdupois ounce. In 
the cleanest parts of the city the number was on- 
ly 10,000,000 per gram, but in the business tho- 
roughfares the average rose4o to 1,000,000,000, and 
in some of the dirtiest streets it reached 5,000,000 
000. In this vast mass of life were many disease 
— producing microbes, and the healthfulness of the 
streets varied with the total number of microbes 
Tests of the infectiveness of the dust gave positive 
results in 73 per cent of the experiments. Of 42 
cases of disease induced in Guinea pigs by inocu- 
lations with the dust of Naples, the microbe of 
pus was found in 8 the bacillus of malignant eda- 
ma in 4, the bacillus of tetanus in 2, and the tu- 
bercle bacillus in 3. Not all city dust has the 
microbe — breeding powers of that of Naples, but 
the difference is believed to be only in degree. 
Geological Notes of Acireale 
BY 
Gaetano Pl ataxia 
III. 
Without occupying myself with the beautiful 
prismatic basalts, sometimes extremely well pre- 
served and at others more or less altered and 
crumbling; nor stopping to describe the fan sha- 
ped sections of the radiated basalts, which form 
splendid natural rock walls, I will devote a few 
words to the globular basalts of Acicastello and of 
these hills. These globular basalts may be divided 
into two categories, namely; firstly the comparati- 
vely large, divided into prismatic wedges, radiating 
from the centre and sometimes articulated, second- 
ly, in globular basalts with a concentric cleavage, of 
most variable dimensions, which sometimes enclose 
foreign rocks. Both are commonly found near me- 
tamorphosed tuff-beds and those nearest to these 
tuffs presents a thin vitreous cracked crust. The 
basaltic globes are often slightly deformed in con- 
sequences of the reciprocal pressure of one against 
another when they were yet in a pasty state. This 
however, does not prevent the general existences 
of variously sized interspaces between them which 
is occupied by clay aud tuff. Of particular interest 
are little globes of about a centimetre in diameter 
which consist externally of a vitreous crust, inter- 
nally of basalt magma with crystals of Olivine, 
i Pyroxenes and Felspar. 
All the basalts of Aci-Trezza and Aci-Castello 
probably due to the injection of magma into a 
thick stratum of submarine silt which occupies, as 
has already been said, the interspaces between the 
different globes. The globular structure is probably 
due to the phenomenon observed experimentally 
by Dr. Johnston Lavis that injecting into a dense 
viscous liquid (in this case the submarine silt) 
another dense liquid (basalt magma) this iatter 
assumes the form of spheres with a narrow neck 
which may be divided leaving the spheres deta- 
ched. Each globe has a different surface of cooling 
which with the consequent contraction extends 
from without inwards and divides the globe into 
a number of radiating wedges. (1.) 
The globes at their periphery in which the cool- 
ing was most rapid are vitrified at the surface, 
being covered by a glassy crust, the formation of 
which was aided by chemical reaction between 
the basalt magma and the clay with which the 
former was in contact. (2.) 
The concentric cleavage which is often exhibited 
by the globular basalts is quite distinct fyom that 
produced by the decomposition due to meteoric 
agencies, as in the of the Balzo to the N. of 
Acireale In this case the blocks of lava are irre- 
gular prisms of lava which shelling and cleaving 
little by little, assume a spherical form until by 
cracking them one encounters a less decomposed 
nucleus. 
In the true globular basalts the globes are pre- 
existent to the action of meteoric agents, andindi- 
pendent of the latter, and the concentric cleavage 
also depends on the process of cooling, the radia- 
ting wedges, dividing into a number of joints, so 
that the crusts, which in consequence of the 
columar cleavage separate into fragments which 
(1) By using a coloured syrup and injecting into 
a. liquid one , the coloured material spreads out in a 
cauliflower fashion but the whole mass looks like so 
many globes. A careful examination of globular 
basalts shows that many arc not simple globes, but 
rather pear shaped masses with a narrow neck 
which is often absent having been divided while 
still fluid. Ed. 
(2) The author probably refers here to the pcla~ 
gonitized layer covering the globesi Ed. 
