In its more limited sense the term "metamorphic" is confined to those changes of rock which are produced directly or indirectly by agencies seated in the interior of the earth. In many cases the mode of change may be explained by our physical or chemical theories, and may be viewed as the effects of temperature or of electro-chemical actions adjoining rocks or connecting communications with the interior of the earth, also distinctly point out the seat from which this change proceeds. In many other cases the metamorphic process itself remains a mystery, and from the nature of the products alone do we conclude that such a metamorphic action has taken place. Serpentine is generally believed to have been originally deposited as a sediment, and to have acquired its present compact crystalline character through the subsequent action of various chemical, or mechanical, agencies. It is known to be a _hydrated silicate of magnesia_ with about equal parts of silica and magnesia, and contains 12 per cent. of water with varying proportions of iron, chromium manganese, alumina and lime, has a specific gravity of 2.7, and weighs about 169 lbs. to the cubic foot. It is found both in a soft and very compact state, of a waxy lustre, with many different shades of beautiful green which give it a mottled appearance like a serpent, hence the origin of its name "serpentine," or ophite. It is called "ranocchia" by the Italians, from the appearance it bears to the "frog," and, on account of its susceptibility to a high polish, is greatly valued as a marble for interior ornamental purposes, more than exterior, as it weathers rapidly. In Galway, Ireland, it is found in large quantities, and called "serpentinous marble," or "ophi-calcite." It is also to be found in other parts of the world, as in the Pyrenees, Alps of Dauphing, Mount St. Gothard, Italy, Sweden, Ural Mountains, Silesia, New South Wales, Savoy, Corsica, Cornwall, Scotland, and other places too numerous to mention; but in Canada the finest and most crystalline serpentine is to be found forming great belts of over 100 miles long and several thousand feet in breadth. There it associates with the dioretic, or volcanic, rocks, and is, according to Dr. Ells, without any doubt, "An alteration product of a dioretic rock rich in olivine." It is sometimes very difficult to distinguish the mineral constituents in many of the metamorphic rocks, but diorite is always considered to be composed chiefly of felspar and hornblende, which composition enters largely into the serpentines. Actinolite, tremolite, &c., and many other minerals, are sometimes found associating with it.