October i, 1890.] 
SiippUment to the “ Tropicol Agyicultuvist.'''' 
division and separation of the parts. The effVst.s 
of the chemical and mechanical causes of the 
decomposition of stone in hiiildiiigs are according 
to their situation, as in the town or country. 
In populous and smoky towns the state of the 
atmosphere accelerates decomposition more than 
in those placed in the open country. 
A great advantage which a country building 
appears to possess over a building situated in 
a populous and smoky town, is owing to lichens, 
with which the country building is almost in- 
variably covered, and which seem to exercise a 
protective influence against the ordinary causes 
of the decomposition of the stone upon Avhich 
they gTow. 
Mineralogists and Geologists enumerate a great 
variety of stones, but the Architect and Engi- 
neer recognise but three great divisions, known 
as “ Freestone, Slab.stone, and Eubblestone.” 
' Freestone. — The name of this stone is derived 
from the freedom with, which it is worked, one 
of its leading characteristics is, that though 
durable against weather, it is yet soft enough 
to be worked with th.e mallet and chisel. It 
is therefore particularly valuable for purpose.®, 
such as columns and their capitals, cornice, frieze 
and mouldings, or for the building of walls, 
where external surfaces are desired. The follow- 
ing are the different varieties of Freestones : — 
1. Marble is one of the primitive limestones, 
being a carbonate of lime, and wdien jmre is 
perfectly white. On account of its durability, 
its non-absorption of water, the ease with which 
it is worked and the high polish it takes, it 
ranks fir.st amongst the freestones. 
2. Alabaster is a fine white stone resembling 
statuory marble ; it is a sulphate instead of a 
carbonate of lime, therefr"e not a marble, being 
very brittle and not durable in the open air is 
used for interior ornamental purposes. 
fl. White Sandstone, next to marble in point 
of grain and durability, is the fine white sand- 
stone, which is composed of a fine silicious sand 
held together liy a peculiar natural cement, so 
fine that it cannot .-e i^crceived between the 
grains. It bears line carving, is strong and dura- 
ble, and not affected by the weather. 
4. The Oolite, so called from its resemblance 
to the roe of a fish, is of a yellowish white colour, 
its grains vary from the fineness of san.d to the 
size of peas, united by a natural cement rpiite 
visible to the naked eye, it is very soft at first 
but hardens from exposure. It is used for build- 
ing purposes solely on account of its fine grains. 
o. The Ferru(/inous or lied Sandstone con.sists 
of a coar.se silicious sand, cemented by an oxide 
of iron. This .stone likewise acquires hardness 
by exposure to the open air ; it is well adapted 
for bridge building, especially in arches of large 
span. 
(1. Soapstone will stand great heat, and is 
therefore a])plicable for fire places and chimney 
jiieces, A'C., but is too soft for building With.' 
7. Granite ranks amongst the most hard and 
durable stones. It bids defiance to the saw and 
almost to tlie chisel, but still it can be worked, 
with expense, to any form, to a fair but not a 
smooth surface. 
Slabstone is of a ciiaracter which sjdits into 
parallel ])lates : it ])Ossesses great strength in 1 he 
direction of its lamiiuv. This stone must always 
be u.sed with its natural joints in a horizontal 
position. It is especially used for flooring and 
covering of roofs, or in the foundation of ex- 
tensive buildings, as being flat and affording 
equal ynessure oil a large surface of ground. 
llubblestone is of a ciiaracter which splits into 
from their hardjiess cannot be sawn, and from 
their brittleness and irregularity of grain re.sist 
all attempts to reduce them to regular shapes, 
save by very expensive processes. These stones 
are only used for rough Avork in foundations, or 
filling in Avails of more than ordinary thickness, 
backing and strengthening tiiem in parts not 
exposed to vieAAA 
(To be conti lived). 
« 
THE GAEDEIS^ SPIDEE. 
The Spider belongs to the class Arachnida of 
the sub-kingdom Annulosa. The true spiders 
(Araneida) is distinguishable as having no true 
antenuae, aud the head and thorax amalgamated 
into a “ cephalothorax.” The sjiider after birth 
undergoes no trajQsformation, and merely in- 
creases in size, though it changes its skin re- 
peatedly before attaining maturity. 
The web of the Garden Spider, though Aory 
AA-onderful in construction, is so familiar that 
a description of it Avould be superfluous. The 
material of which the Aveb is made is the 
secretion of a special gland, and it is moulded 
to its proper shape by being passed through 
certain conical little organs Avhich are placed at 
the extremity of the abdomen, and are terme<l 
the “spinnerets.” The apex of each S]nnneret 
is perforated liy a large number of little holes. 
The silk is at first fluid, but hardens rapidly 
on exposure to air. A single filament of .sillc 
is thus produced by each of the perforations in 
the .spinneret, .so that Avhat is called a single 
“thread” in a spider's Aveb is really a cable, 
composed of a great number of the most delicate 
fibres agglutinated together. The Avebs of the 
Garden Spider are almost alAA^ays simn lietween 
the leaA'es of a plant or in the space betAveen 
two or three plants situated in close proximity. 
The elasticity and strength of the material of 
the Aveb is proved by the fact that it is un- 
injured by a strong breeze. Should a thread 
he broken by a violent gust of Aviud or some 
other nulooked-for accident, the .spider effects 
the necessary repair almost immediately. By a 
singular instinct the spider prevents the Aveb 
from being unduly stretched Avith the chance of 
snapping, by hanging pieces of wood or pebble 
to gh’e it Aveight. The spaces in the AA’eb con- 
tains a .sticky substance Avhich is intended to 
eutra]) insects by their legs or Avings. The 
S]iider kills its prej* not by a sting like that 
of the scorpion, but by a pair of strong hooked 
jaAA’s (poison jaAvs) Avhich have their points per- 
forated for the escape of a poisonous fluid 
secreted by .special glands. As is generally 
known all spider- are carnivorous, but the point 
of interest about the Garden Spider is that the 
flies and insects it captures and kills are nearly 
all injurioTis to Aegetatiou. Langsdorf goes the 
lengtli of saying that Miji/ale avicnlaria, a Garden 
Spi<ler, only eats insects injurious to vegetation ! 
At any rate there seems sufticient reason fov 
