Petrographically tuffs are classified according to the nature of the volcanic rock of which they consist ; this is the same as the accompanying lavas if any of these were emitted during an eruption, and if there is a change in the kind of lava which is poured out, the tuffs indicate this equally clearly. Rhyolite-, trachyte-, andesite-, and basalt-tuffs are thus the most frequently occurring pyroclastic rocks of the present day. Tuffs are well represented in the stratigraphical record ranging from the Pre Cambrian to Recent. The older tuffs are most often greatly changed by silicification and devitrification. They may be com pletely metamorphosed with loss of all original textures and can then only be recognized by their chemical composition and field relationships. Many chlorite and hornblende schists in meta morphic regions represent recrystallized ash beds of basaltic character. The Swedish halleflintas (q.v.) include rocks of pyro clastic origin of the nature of rhyolite-tuffs, but they are com pletely changed by recrystallization to a granular assemblage of quartz, felspar, mica, etc. (See also VOLCANO.) ( J. S. F.) TU FU (tta , A.D. 713-770), a Chinese poet and painter of the Tang dynasty, considered by some Chinese critics as the supreme poet. Tu Fu was born in Tu Ling in the Shensi prov ince, and is therefore often called Tu Shao-Ling (it/(), although his father was a native of Hsiangyang in Hupeh. His family belonged to the military and literary class. At 15, his essays and fantastic verses won great admiration. After ten years of wandering, he went to the capital, Changan ( ), for his literary examinations. Although his written papers were excellent he was not given a degree, as his views were unorthodox.
He then became a wanderer, and on the "Lute Terrace" in Ching Hsien, he met his much admired friend Li Po, whom he immortal ized in verse.
In 749 the emperor invited all great scholars for ex amination. Tu Fu presented himself, but waited for four years until he managed to please the emperor with his three great fu (Ejali , a prose poem of irregular lines). He was given a post in the Chih Hsien library which he held for four years, he was then promoted to another post at Feng-hsien. In 758, when the rebellion of An Lu-Shan which drove the emperor Ming Huang from the throne, broke out, he was exiled and went to live with a relative at White Water village ( Ai ) When a new emperor ascended the Dragon throne, Tu Fu went to pay his respects to him, but on the way he was captured by brigands, beaten, and made prisoner for a year. He escaped, and, emaciated and clad in rags, he reached the emperor. He was appointed to the post of censor, but fell into disgrace and was delegated to a minor post as governor of a small town in Shensi. This position he did not accept, and joined his family at Kansu. They were struggling for existence, and the poet sup ported them by digging up roots for food and by selling fire wood. Several of his children, however, died of hunger. After six months in office in Hua Chou, he retired to Chengtu in Szechwan, living in a house of grass roots. Here he wrote some of his most beautiful lyrics.
In 768 he took up nomadic life once more. He was caught by floods and compelled to go into a ruined temple at Hu Huang without food. After ten days' starvation he was given a feast by the local officials, and died (77o) of over-eating.