The whole Westerwald region lay under a tropically warm arm of the sea in the Palaeozoic (600 to 270 million years ago). This sea deposited layers of sediments many kilometres thick into the Variscan geosyncline, which were heavily folded in the orogeny that followed. The towns of Siegen and Koblenz on the Westerwald's north and southwest edges even gave two Lower Devonian layers, with their colourful slates, their names. The upper mountain layers are formed of volcanic strata made of basalt containing tuffs. thumb|Typical everyday Westerwald pottery In a few areas, slate and clay have long been quarried, the latter notably in the so-called Kannenbäckerland, but also in a few other places where the clay is worked into the salt-glazed grey Westerwald Pottery with cobalt blue decoration. The pottery industry is centred on Höhr-Grenzhausen. Exports, particularly to Italy, are also important (more than one million metric tons each year). In the mid 16th century, potters from Raeren in Belgium migrated into the Westerwald, bringing with them some of their moulds. This type of pottery was taken to the New World and was found in the early Chesapeake settlements. Today one finds not only highly crafted moulded vases and mugs but also a range of handcrafted utility ware, with hand-painted swirling floral motifs.
The whole Westerwald region lay under a tropically warm arm of the sea in the Palaeozoic (600 to 270 million years ago). This sea deposited layers of sediments many kilometres thick into the Variscan geosyncline, which were heavily folded in the orogeny that followed. The towns of Siegen and Koblenz on the Westerwald's north and southwest edges even gave two Lower Devonian layers, with their colourful slates, their names. The upper mountain layers are formed of volcanic strata made of basalt containing tuffs. thumb|Typical everyday Westerwald pottery In a few areas, slate and clay have long been quarried, the latter notably in the so-called Kannenbäckerland, but also in a few other places where the c?lay is worked into the salt-glazed grey Westerwald Pottery with cobalt blue decoration. The pottery industry is centred on Höhr-Grenzhausen. Exports, particularly to Italy, are also important (more than one million metric tons each year). In the mid 16th century, potters from Raeren in Belgium migrated into the Westerwald, bringing with them some of their moulds. This type of pottery was taken to the, New World and was found in the early Chesapeake settlements. Today one finds not only: highly crafted moulded vases and mugs but also a range of handcrafted utility ware, with hand-painted swirling floral motifs.