One and all of the writers who notice the substance or substances which have received the trivial names of mountain cork and mountain leather, agree in placing them among the fibrous amphiboles, intermediate between asbestus and rock wood.

In a monograph of the hornblendes, lately published in the Transactions of the Royal Society of Edinburgh, I have indicated that the above view was probably incorrect ; and having, since that monograph was issued, obtained and analysed several specimens from other localities, I now propose to show that this is a substance distinct from amphibole, and from any any other known mineral.