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serpentine, or the opaque varieties forming rock masses, like those of the Lizard, Portsoy, Anglesea, and Zoblitz. 3. Fibrous serpentine, including balti- morite, crysotile, metaxite, picrolite. 4. Foliated serpentine, comprising antigorite, marmolite, 1 &c. To the above might be added eozonal serpentine; and loganite, of Dr. Sterry Hunt. Composition and Origin. Pure serpentine is a hydrated silicate of magnesia; but as a rock it is generally mixed or interlaced with carbonate of lime, diallage, dolomite, steatite, and other foreign sub stances. Its origin by a process of metamorphism, or transmutation, from dolomite, diorite, hornblende rock, and gabbro, 2 is now generally recognised, though formerly it was regarded as a product of igneous fusion. 8 Breithaupt first detected serpen tine under the crystalline form of hornblende, and 1 Bristow, Glossary of Mineralogy (1861). 2 This view of transmutation from igneous rocks probably offers a sufficient explanation of the phenomena exhibited by the ser pentine of the Lizard in Cornwall and other districts, where it has the appearance of an erupted mass in relation to the surrounding rocks. Those who are interested in this subject should make themselves acquainted with the experiments and observations of Mr. A. Gages, M.R.I.A., published in Reports to the British As sociation, entitled ‘ Special Researches on the formation of Mine rals,’ 1862 and 1863. 3 That this was the opinion of so eminent an observer as Sir H. De la Beche in 1839 will be seen by reference to his work on Devon and Cornwall, p. 30. This opinion was probably after wards modified.