TRASS  , the

local name of a volcanic tuff occurring in the Eifel, where it is worked for hydraulic mortar . It is a grey or cream-coloured fragmental rock, largely composed of pumiceous dust, and may be regarded as a trachytic tuff . It much resembles the Italian puzzolana and is applied to like purposes . Mixed with lime and sand, or with Portland cement, it is extensively employed for hydraulic work, especially in Holland; whilst the compact varieties have been used as a building material and as a fire-stone in ovens . Trass was formerly worked extensively in the Brohl valley and is now obtained from the valley of the Nette, near Andernach .