Architectural variety and solidity are favoured in the buildings of the city by a wealth of beautiful building stones of varied colours (limestones, sandstones, lavas, granites and marbles), in addition to which bricks and Roman tiles are employed.
The first eruptions piled up huge domes of lavas rich in soda, including the geburite-dacites and sOlvsbergites of Mount Macedon in Victoria, and the kenyte and tephrite domes of Dunedin, in New Zealand.
Lavas dip in all directions from the central crystalline core, pointing to the conclusion that the main portion of the mountain represents a single volcanic mass.
In the southern region of unfolded beds are found the lavas of the " harras " of Arabia, and in India the extensive flows of the Deccan Trap. In the central folded belt lie the great volcanoes, now mostly extinct, of Asia Minor, Armenia, Persia and Baluchistan.
The chlorite-schists are often of igneous derivation, such as ash-beds or fine lavas which have been metamorphosed.