100 DOLOMITE FAMILY. contains imbedded portions of quartz, dolomite-spar, and sparry iron-ore *. Geographic Situation. It occurs in Nottinghamshire, Derbyshire, Northamp tonshire, Leicestershire, Northumberland, and Durham"f: also in Ireland, at Portumna in Galway, Ballyshannon in Donnegal, Castle Island near Killarney +. It has been observed among the limestone rocks near Erbefeld and Gemarek, in Westphalia ||. It also occurs in veins, as in those of Derbyshire, where it is associated with galena §. Uses. Like common limestone, it is burnt and made into mortar, but it remains much longer caustic than quick lime from common limestone; and this is the cause of a very important difference between magnesian and com mon limestone, with regard to their employment in agri culture : Lime, from magnesian limestone, is termed hot, and when spread upon land in the same proportion as is generally practised with common quicklime, greatly im pairs the fertility of the soil; and when used in a greater quantity, is said by Mr Tennant to prevent all vegeta tion . Second * Berger, Geological Society Transactions, vol. II. p. 44. -f- Grecnough. * Greenough. [[ Boumon, Traite de Mincralogic, t. i. p. 2(18. § Bournon, Traite, lb. In regard to this limestone, Dr Thomson has the following remarkss “ This mogneaian limestone has been long burnt in prodigious quantity in rhe
