" Lean-to," " shed," or " pent " roofs are practically developments of the flat roof, one end of the joists (which are now called " rafters ") being tipped up to form a decided slope, which enables slates, tiles, corrugated iron and other materials to be employed which cannot be used upon a " flat " roof.
Iron goods of various kinds, glass and pottery, school slates, pencils and marbles are produced; the abundant timber fosters the manufacture of all kinds of wooden articles, especially toys; and the textile industry and the manufacture of leather goods, papier mache and sewing-machines are also carried on.
There were many places covered by limestone.
The Cambrian is represented by blue clays, ungulite sandstones and bituminous slates in Esthonia and St Petersburg.
In the centre of the folds fossiliferous beds with crinoids have been found, and the black slates at the top of the series contain Myophoria and other fossils, indicating that the rocks are of Triassic age.
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