Volltext Seite (XML)
INTRODUCTION. xxvii A fpecies Is compofed of a greater or leffer number Specie*, of varieties. If in a fpecies we meet with groups of varieties that can be well diftinguifhed from each other, we mud g:ve them a particular appellation ; Werner de nominates them fubfpecies. suMpeeie*; lo illuftrate the manner of forming fubfpecies, we Mo(! . e<>f /Tiij . forming ihall take an example from the clafs of metals; it is fubfpecies lead glance which contains two fu’ fpecies, ‘a. Com mon lead glance, b. Compaff lead glance. Ihe elfential character of the fpecies is as follows: Colour lead grey. Luftre metallic. Streak unchang ed. Mild. Soft. Very heavy. Firfl Subfpecies. Common lead glance Has fometimes particular external fliapes as reticu lated, cellular, tubular, &c. It is often cryftallifed. Luftre almoft always finning, fometimes 1 'fplendent.. radlure more or lefs perfe&ly foliated, generally nraight, often curved foliated, with a threefold cleav age, feldom radiated and ufually flrort, broad, and fcopiformly diverging radiated. .Very eafily frangi ble. ' Second 'Subfpecies. Com pad lead glance. Colour is lighter than the preceding fubfpecies. ccurs only maffive and fpecular; has no particu- ar extern al fhape. Luftre only glimmering. Frac ture even. Fragments indeterminately angular. Does not oc cur in diitindt concretions. Has more tenacity than the preceding fubfpecies. When an extenfive fpecies is undivided, it is not only difficult to fix the piflure of it in the mind, but d 2 the