to each other.  Messrs. Wall and Sawkins explain the odd fact clearly and simply.  The oil, they say, which the asphalt contains when it rises first, evaporates in the sun, of course most on the outside of the heap, leaving a thorough coat of asphalt, which has, generally, no power to unite with the corresponding coat of the next mass.  Meanwhile Mr. Manross, an American gentleman, who has written a very clever and interesting account of the lake, seems to have been so far deceived by the curved and squeezed edges of these masses that he attributes to each of them a revolving motion, and supposes that the material is continually passing from the centre to the edges, when it “rolls under,” and rises again in the middle.  Certainly the strange stuff looks, at the first glance, as if it were behaving in this way; and certainly, also, his theory would explain the appearance of sticks and logs in the pitch.  But Messrs. Wall and Sawkins say that they have observed no such motion:  nor did we; and I agree with them, that it is not very obvious to what force, or what influence, it could be attributable.  We must, therefore, seek some other way of accounting for the sticks—­which utterly puzzled us, and which Mr. Manross well describes as “numerous pieces of wood, which, being involved in the pitch, are constantly coming to the surface.  They are often several feet in length, and five or six inches in diameter.  On reaching the surface they generally assume an upright position, one end being detained in the pitch, while the other is elevated by the lifting of the middle.  They may be seen at frequent intervals over the lake, standing up to the height of two or even three feet.  They look like stumps of trees protruding through the pitch; but their parvenu character is curiously betrayed by a ragged cap of pitch which invariably covers the top, and hangs down like hounds’ ears on either side.”

Whence do they come?  Have they been blown on to the lake, or left behind by man? or are they fossil trees, integral parts of the vegetable stratum below which is continually rolling upward? or are they of both kinds?  I do not know.  Only this is certain, as Messrs. Wall and Sawkins have pointed out, that not only “the purer varieties of asphalt, such as approach or are identical with asphalt glance, have been observed” (though not, I think, in the lake itself) “in isolated masses, where there was little doubt of their proceeding from ligneous substances of larger dimensions, such as roots and pieces of trunks and branches,” but, moreover, that “it is also necessary to admit a species of conversion by contact, since pieces of wood included accidentally in the asphalt, for example, by dropping from overhanging vegetation, are often found partially transformed into the material.”  This is a statement which we verified again and again, as we did the one which follows, namely, that the hollow bubbles which abound on the surface of the pitch “generally contain traces of the lighter portion of vegetation,” and “are manifestly derived from leaves, etc., which are blown about the lake by the wind, and are covered with asphalt, and, as they become asphalt themselves, give off gases which form bubbles round them.”