’ 15 
and vegetable, is readily proved. The polished appearance of a 
stem of wheat is owing to silica; the leaf blades of some of the 
coarser grasses are so highly charged with it that they draw blood 
when passed rapidly between the fingers; the Hquisete or horse- 
tails contain so much that a polishing powder is made from their 
ashes; the leaf hairs of some plants are wholly siliceous ; while 
from the interior of one of the bamboos of India large lumps are 
sometimes taken in the form of Tabasheer, a more highly refract- 
ing substance than even the diamond. Of course all this is 
extracted by the plant from the soil. 
In the animal creation its abundance is more remarkable still. 
Countless species of the microscopic foru.s known as diatoms con- 
struct their exquisitely beautiful shells from the silica yielded by 
the waters in which they live. You can examine some of these for 
yourselves in the microscopeson the table. Enormous areas of the 
bed of the Pacific were found by the Challenger to be covered with 
siliceous, i.e., flinty deposits, consisting chiefly of Radiolaria. Some 
were brought up by the dredge from a depth of five miles. Mingled 
with them were the ‘spicules’ of sponges. These are minute 
needle shaped bodies composed of silica, supporting the soft frame- 
work of animal matter forming the sponge. Thus silently, and 
hidden from the eye of man, the processes of nature are carried on 
~ in almost abysmal depths, laying the foundations of future worlds 
and writing in indelible characters the history of their own times. 
Other sponges anchor themselves to the mud or rocks of the ocean 
bed by ropes of siliceous fibres, rising up by a single long chimney- 
like tube. See the Euplectella before you.— Venus’ Flower Basket, 
“without any exception one of the most exquisite of all organic 
structures known to us.” In its living condition this skeleton, 
which is wholly silica, is completely covered by a thick coating of 
animal matter called by zoologists sarcode. Another family includes 
‘the Hyalonema or glass-rope sponge, which ‘has the lower portion 
of its siliceous rope-like axis exactly like a skein of threads of glass, 
and is sunk in the sand at the bottom of the sea.” This is a rarer 
form judging by the price asked for it at present (two pounds), but 
you will find an illustration of it, and also of its beautiful spicules, 
in the volume of Science Gossip on the table. — (Vol. for 1872, p. 36) 
Now, remembering all this, and then noticing the very frequent 
occurrence of sponges and their spicules, shells, and other animal 
remains in flint, we are led to make a shrewd guess that life in 
some form or other had to do with its formation. A very large 
proportion of those flints of curious shape on every wayside heap— 
- semi-globular, spherical, cup-like, branched, &c., will be found to 
have fossil remains inside. Frequently a dexterous blow of the 
_ hammer separates the flint symmetrically, and numbers of spicules, 
