Slates are not so much used in our schools as they were years ago, exercise-books being cheaper now. Still, there are some schools where the children have slates, and pocket-books are to be bought, containing a slate tablet, on which you can write notes, and rub them out afterwards to make fresh ones. Slates upon the roofs of houses are objects familiar to us all. Probably few, young or old, who have to do with slates, ever think what this substance is, and where it has come from. Yet slate is one of the most wonderful things in this world of ours.

Supposing the first question put to us was, 'What is slate?' our answer would be, 'It is simply a sort of dried mud.' If the second was, 'What is its place amongst the rocks of our earth?' we should say, 'Slate belongs to the Cambrian formation.' This is a big series of rocks, sometimes eighteen thousand feet thick. It contains in the middle what geologists call flags and grits, but the larger part of it is slates. There is but one series of rocks more ancient than the Cambrian, and that is the one called the Laurentian, which is said not to be found in Britain.

'Cambrian,' some might say: there is a reason for that name, which of course is only another word for Welsh. Though, in their first order, these slaty rocks lie deep down, they have been lifted high up, and they show us some of the grandest scenery we have in this island. The hills and precipices of Wales, and the hollows where the mountain streams flow, tell of the shakings and twistings that the Cambrian rocks have gone through. Amongst them grow ferns and rare flowers, while many a tourist draws in new strength as he mounts them. Sometimes, high up, the rains and winds have made the rocks so bare that even mosses cannot live upon them, and in the clear sunlight the slates appear of various shades, from pink to deep blue.

One curious thing about slate is that the layers are often twisted or wrinkled. This has been caused, partly at least, by their being thrust up when half hardened, so as to cause a sort of fold or crease. This was chiefly done by the still harder granite.

It is wonderful to think of the succession of plants and animals that slate has had to do with; it was in existence when the coal forests were forming, and it must have been trodden by the strange creatures of other strata, which are now extinct, but of which relics are dug up. Another remarkable fact is that the slate-beds have had wonderful ups and downs over and over again during the earth's changes—being at one time under a deep sea, at another lifted to form hills, as we frequently see them now.