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 46 SILLOWAY publication of its " Proceedings." He is also ,!ar lecturer. Besides numerous papers in the M Aiiu-ri.-uii Journal of Science," ho has published " First Principles of Chemistry,' a popular text l.u-k (Philadelphia, 1846; revised ed., 1856), and "Principles of Physics" (Phila- delphia, 1858 ; revised ed., 1868). MI.I.OMU, Thonia* Nilliam, an American ar- chitect, born in Newburyport, Mass., Aug. 7, 1828. He lieirari to practise his profession in Boston in 1851, and in the 20 years following more than 200 church edifices were built or reinodelK'l un.ler his superintendence. He de- signed the new capitol, Montpelier, Vt. (1859), Buchtel colle-c, Akron, O. (1872), &c. While pursuing his profession as an architect, he act- ed as a Universalist preacher from 1852, and was ordained a clergyman in 1862. He has published "Theognis, a Lamp in the Cavern of Evil " (Boston, 1856) ;. " Text Book of Modern Carpentry" (1858); "Warming and Ventila- tion" (1860); "Atkinson Memorial," a series of 18 discourses (1861) ; " The Conference Mel- odist" (1863); "The Cantica Sacra," a book of church service (1865) ; and " Service of the Church of the Redeemer" at Brighton (1867). With George M. Harding he edited an improved edition of Shaw's " Civil Architecture " (1852). SILPIIHM (Gr. oityiov, the ancient name of some resin-bearing plant), a genus of coarse, robust, perennial plants of the composite fami- ly, which have a copious resinous juice and large heads of flowers, resembling those of the sunflower, but quite different in structure. In sUl>hium the numerous ray flowers are pistil- late and fertile; those of the disk, though they are apparently perfect, are sterile; the broad flat akenes are winged and without pappus. The genus comprises about 20 species, all North American; some are very abundant on the western prairies, while others are peculiarly southern. The best known species is S. lacini- atum, called rosin weed ; it has a large thick root, from which arise numer- ous radical, long-pe- tioled leaves, from 12 to 80 in. long; they are very thick, and rough with bristly hairs ; their general outline is rate, but they are deeply pinnatcly cut and parted, and the divisions themselves often '10 stem, usually 3 to 6 ft. high ometimes reaches 11 ft., and bears near its >aae numerous leaves similar to those from the root, and fewer leaves above. The flower Botia Weed (Sllphlum laclnU- turn). SILURIAN heads, borne in a kind of raceme at the upper part of the stem, are 3 to 5 in. across, and, as in all the other species, yellow. The resiuous juice of this and others exudes either sponta- neously or from the puncturing of insects, ap- pearing in small translucent tears upon the stem and foliage. This resin and the plant it- self have been regarded as useful remedies in asthma and similar diseases of horses. A tinc- ture of the root and leaves is sometimes used as a domestic tonic and diaphoretic. The erect leaves of this plant, Avhen growing in the open prairie, commonly stand with their edges point- ing north and south ; hence it has been called compass plant, pilot weed, and polar plant. This species occurs from the prairies of Mich- igan southward and westward. A closely re- lated species, found from Ohio west and south, called prairie burdock or prairie dock, is S. terebinthinaceum, having also large and coarse leaves, which are not cut, but only serrate on the margins, and rough and scurfy especially on the under surface ; the tall stems are smooth, and the heads of flowers are smaller than in the preceding. This species produces resin abundantly, the leaves being often sprinkled with it. One of the most striking species is S. perfoliatum, calle'd the cup plant ; its square stem bears opposite leaves, a foot or more long ; these are united by their bases around the stem, and form a concave disk, which after a rain contains a considerable quantity of wa- ter. This has a similar geographical range to the preceding, but having long been cultivated in gardens on account of its curious leaves, it has been introduced much further east. SILURIAN, the name of one of the geologic ages, the age of mollusks and other inverte- brates. The name is derived from that of the ancient Silures, who inhabited that portion of England and Wales where these rocks abound. The formation lies upon the Cambrian of Sedg- wick, according to some classifications, and im- mediately below the Devonian. Murchison in- cludes in it the upper Cambrian of Sedgwick. The subdivisions of the Silurian age differ in Europe and America, and also in different parts of the same continent. In North America the transition of the rocks and life from the lower to the upper Silurian is abrupt. In Great Brit- ain the transition in life is gradual, although the rocks are unconformable in stratification. In Bohemia there is no break in the rocks, but there is marked change in the life. Dana has adopted the subdivision into periods and epochs derived from the succession of rocks in the state of New York, where the strata are well displayed, and have been carefully studied. In this arrangement the lower Silurian, begin- ning from below, includes the primordial or Cambrian, the Canadian, and the Trenton peri- ods ; the upper Silurian embraces, in the same ascending order, the Niagara, Salina, lower Helderberg, and Oriskany periods. The Oris- kany formation was until recently placed as the lowest period of the Devonian age ; but from