Deodat Gui Sylvain Tancrede De Gra-Tet De Dolomieu, a French geologist, born at Dolomieu, Dauphiny, June 24, 1750, died at Chateauneuf, department of Saone-et-Loire, Nov. 26, 1801. When 18 years old he killed in a duel a knight of Malta, of which order he was himself a member. He was condemned to death, hut the sentence was commuted to imprisonment for nine months, and in his dungeon he devoted himself to the natural sciences. On recovering his liberty he obtained a commission in the army, but did not relinquish his scientific investigations, of which the first fruits appeared in 1775 in his Recherches sur la pesanteur des corps d differentes distances du centre de la terre. Made a corresponding member of the academy of sciences, he abandoned the military profession and devoted the rest of his life to science. For a series of years he was engaged in exploring Portugal, Spain, Italy, and afterward Egypt, whither he went with Bonaparte's expedition. While on his return to Marseilles in 1799 he was seized by the Neapolitans, and through the enmity of the order of Malta detained in prison at Messina, where, amid extraordinary hardships, he wrote his Traite de philosophic mineralogique, and his Memoire sur l'espece minerals.

He recovered his liberty March 15, 1801, with impaired health, and died soon afterward, while on a visit to his sister. The results of his researches are embodied in his contributions to the Journal de Physique, Journal de l'In-stitut, Journal des Mines, etc. More than 50 distinct memoirs, many of which contain valuable additions to the knowledge of geology and mineralogy, can thus be traced to his pen, besides his contributions to the Dictionnaire, mineralogique and the Nouvelle Encyclopedie. His most interesting essays are: Memoires sur le tremblement de la terre de la Calabre; Voyage aux iles de Lipari; Memoires sur les iles Ponces, et Catalogue raisonne des produits de l'Etna; and on the nature of leucite, anthracite, pyroxene, etc. The Journal du dernier voyage du citoyen Dolomieu dans les Alpes was published by Bruun-Neergaard at Paris in 1802. DOLOMITE, a mineral species named in honor of the French geologist Dolomieu. It occurs crystallized in rhombohedral forms, and also as a rock of granular and crystalline structure. The mineral species includes several varieties, as brown spar, pearl spar, etc. Its hardness is 3.5-4; specific gravity, 285-2.92. The weight of a cubic foot of the rock is consequently about 180 lbs.

Dolomite is a magnesian carbonate of lime, consisting of one equivalent of carbonate of magnesia and one of carbonate of lime, or, in 100 parts, 45.65 of the former and 54.35 of the latter. It is usually white, but is also found of various colors. It is largely developed as a metamorphic rock in the calciferous epoch of the Potsdam period of the Silurian age, and is found abundantly along the eastern part of the middle states, its range extending through the gold region of the southern states, northward, passing near Washington, Baltimore, and Philadelphia, thence crossing northern New Jersey, and to the south of the highlands across the Hudson, through western Massachusetts and Vermont into Canada. It also occurs at many localities to the eastward of this metamorphic range. It is very extensively developed in the Tyrolese mountains, Austria, and in various parts of Europe. A beautiful white dolomitic marble used by the ancient sculptors is found in the island of Tenedos, near the west coast of Asia Minor. A brown dolomite, the magnesian limestone of Tennant, occurs in the north of England in beds of considerable thickness, resting on the Newcastle coal formation.

In the Isle of Man it is found in a limestone resting on graywacke, and it occurs in trap rock in Fifeshire. Columnar dolomite is found in metamorphic rocks in the Niagara group, in the upper Silurian formation in western New York, and in serpentine in Russia. - For agricultural purposes magnesian lime is not as highly valued as pure lime. It enters less largely into the composition of most cultivated plants, and is thought to render the soil less friable. For making mortar there is a difference of opinion, the European masons rejecting it, while it is popular in the United States. As a building stone, dolomite ranks among the best, as it is easily worked and very durable. It is obtained in large blocks of sound and uniform texture, with good grain for splitting, and unmixed with foreign matters. But different layers in the same quarry vary greatly in quality. The softness of the stone admits of its being easily sawn into ashlar and carved into ornamental mouldings. In England, dolomite has proved so durable and excellent, that a variety of it found at Bolsover moor was selected for the new houses of parliament.

The choir of Southwell church, which was built of this variety of stone in the 12th century, was found by the commissioners to be in so perfect a state that " the mouldings and carved enrichments were as sharp as when first executed." After describing other examples illustrating the durability of this rock, the commissioners say: "As far as our observations extend, in proportion as the stone employed in magnesian limestone buildings is crystalline, so does it appear to have resisted the decomposing effects of the atmosphere; a conclusion in accordance with the opinion of Professor Daniell, who has stated that, from the results of experiments, he is of opinion that 'the nearer the magnesian limestones approach to equivalent proportions of carbonate of lime and carbonate of magnesia, the more crystalline and better they are in every respect.' " The following analyses of some of the best of the American dolomites show how nearly they correspond in composition to the requisite of Professor Daniell:

MARBLE OF

ANALYZED BY

Carbonate of lime.

Carbonate of magnesia.

Hastings, N. Y..

J. W. Draper, M.D..

52.82

45.78

Sing Sing, " ..

Lewis C. Beck, M.D.

53.24

45.89

Tuckahoe, " ..

" "

61.75

38.25

Roxbury, Vt....

T.S.Hunt..........

53.90

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