Supplement to the "Tropical Agriculturist." [October i, 1889. 
2g8 
a geological survey, there will accrue a vast amount 
of invaluable knowledge to agriculture as well as 
to many other industries. To the agriculturist a 
knowledge of the sub-strata of his land will be of 
great value; helping him to find out the nature of 
the formations beneath, and whether any are absent ; 
the dip of the beds and their thickness, as well as the 
arraugement of the permeable and impermeable strata. 
Information of this nature will help him in such 
operations as drainage, irrigatiou, and water supply. 
LIFE-HISTORIES OF INSECTS INJURIOUS 
TO VEGETATION IN CEYLON. III. 
By Aba. 
Saving explained the general principles of Ento- 
mological science in the previous articles, I will now 
proceed to discuss the classification of Insects. Linne 
in his Systema Natura: divides all insects into seven 
great orders, viz : Coleoptera, Hemiptera, Lepidoptera, 
Peuroptera, Hymenoptera, Diptera and Aptera. Several 
modifications were proposed by Leach and other 
authors, but the classification, adopted by Prof. "West- 
wood in his " Introduction to Entomology, " which 
divides all insects into thirteen orders is accepted on 
all sides as the most simple and comprehensive system. 
In the words of Miss Ormerod the thirteen orders are 
"arranged according to general similarity in the 
early stages, and also in the general appearance of 
the perfect insects composing each order; also accord- 
ing to the number or nature of their wings, or the 
method in which they are folded beneath the wing- 
cases." 
These thirteen orders of Westwood are divided into 
two great tribes named Mandibidata and Haustellata. 
To the firstnamed tribe belong the inseots which feed 
by means of jaws (Mandibles) such as the Beetles, &c. 
To the second belong the moths, butterflies, aphides, &c. 
insects which feed by means of a kind of sucker 
(haustellumV 
"With regard to the nomenclature of the orders it 
will be noticed that the last part of the name of each 
order is Ptera, which comes from the Greek word 
Pieron, a wing, while the first part describes the nature 
of the wing, for example, Coleo — (sheath) ptera (wing) 
the order of beetles. 
The following list of the orders oE insects is taken 
from the " Manual of Injurious Insects " by Miss 
Ormerod : — 
Mandibulata. 
Coleoptera.— Sheath-winged. Beetles. 
Euplexoptera.— Lightly-folded wingled. Earwigs. 
Orthoptera.— Straight-winged. Cockroaches, crickets, 
grass-hoppers, &c. 
Thysanopteni.— Fringe-wined. Thrips. 
Neuroptora.— Nerve-winged. White ants, May-Mies, 
Dragon flies, &c. 
Trichoptera.— Hairy-winged. Caldice-flies. 
Hymenoptera. — Membrane-winged. Saw-flies, Gall- 
flies, aDts, wa6p6, bees, &c. 
Strepsiptera. — Twisted- winged. Bee parasites. 
HansteHata. 
Lepidoptera. — Scale-winged. Bulterflies, Moths. 
Homoptera. — Similar-winged. Aphides, Scale-insects. 
&c. 
Heteroptera. — Dissimilar- winged. Plant-bugs, &c. 
Aphaniptera. — Imperceptible- winged. Fleas. 
Diptera. — Two-winged. Gnats, Gad-flies, Bot-flies, 
Flesh-flies, &c. 
(To be continued.) 
- 4, 
NOTES ON SOME OF THE GEOLOGICAL 
FOBMATIONS IN CEYLON. 
By C. Deiebebg, b.a., f.h.a.s. 
Clay, a common formation in Ceylon, is a product 
from the decomposition of highly felspatic rock such 
as granite. It consists mainly of silica and hydrated 
silicate of alumina with also variable proportions of 
other ingredients. Taking granite as a source of clay 
we observe that it is formed mainly of three minerals : 
quartz, felspar and mica. Quartz is nearly pure silica ; 
felspar is essentially composed of silica, alumina and 
potash; while mica may be generally described as 
aluminous silicate containing potash. Now, in all 
these minerals there is a large proportion of either 
silica or alumina or both. In the process of decom- 
position of the granite the silica and alumina unite 
to form silicate of alumina and become further 
hydrated by the addition of water. The two latter being 
the least soluble, are left as the ultimate products of 
decomposition, while the other ingredients of quartz, 
felspar and mica are carried away in solution. Clay 
then consists as before stated of the hydrated sili- 
cate of alumina with such other ingredients of the 
original minerals as have not been carried away in 
solution. Where the result of decomposition is almost 
altogether silica and hydrated silicate of alumina, we 
get kaolin or China clay and pipe clay. Potters 
clay contains more impurities than these, while brick 
clay again consists of a mixture of finely-divided 
clay and fand together with iron. Fire clay contains 
little or no lime and other alkaline eaaths, or iron, 
which under the influence of heat act as fluxes, and 
would thus unfit the clay for the purpose it is in- 
tended to fulfil. Iron ore abounds in certain clay 
deposits as clay iron stone, and also appears often 
as nodules in combination with earthy matter. 
Mr. A. C. Dixon observes that in decomposing, they 
produce a rock identical with laterite or cabook. These 
nodules I observed present to a large extent in the red 
clay soils near Matale, some of them evidently contain- 
ing very large proportions of iron, judging by their 
great weight. Clay slate is a clay deposit which has 
undergone great pressure, and splits readily into thin 
plates or slabs ; it is found of a variety of colours 
The clay state group is included in the metamorphic 
system together with gneiss and mica-schist. 
After the disintegration of the original felspatic 
