Tarras, Terras, or Traas, a species of argillaceous earth, found in Germany, and Sweden, whence it is annually imported ; being subject to the duty of 6 1/2d. per bushel. It is of a pale-yellowish colour, containing numerous particles of spar, and other heterogeneous matters.

When reduced to powder, and mixed with water, terras forms a most durable cement or mortar, which is advantageously employed for lining basons, cisterns, or other reservoirs.

In the 5th vol. of the Transac-tions of the Society for the Encouragement of Arts, etc. for 1787, we meet with a communication by Mr. More, stating, that a species of red earth has been discovered in the parish of St. Elizabeth, Jamaica, which is an excellent substitute for tarras, in all buildings under water. Thus, if one measure of such earth be mixed with an equal portion of sand, and a double quantity of well-slacked lime, the whole will form a cement, excellently adapted for constructing dams, bridges, or any other edifice in wa-ter; as it speedily hardens, and acquires the durability of stone.