As we went onward up the gentle slope (the rise is one hundred and thirty-eight feet in rather more than a mile), the ground became more and more full of pitch, and the vegetation poorer and more rushy, till it resembled, on the whole, that of an English fen.  An Ipomoea or two, and a scarlet-flowered dwarf Heliconia, kept up the tropic type, as does a stiff brittle fern about two feet high. {148a} We picked the weeds, which looked like English mint or basil, and found that most of them had three longitudinal nerves in each leaf, and were really Melastomas, though dwarfed into a far meaner habit than that of the noble forms we saw at Chaguanas, and again on the other side of the lake.  On the right, too, in a hollow, was a whole wood of Groo-groo palms, gray stemmed, gray leaved; and here and there a patch of white or black Roseau rose gracefully eight or ten feet high among the reeds.

The plateau of pitch now widened out, and the whole ground looked like an asphalt pavement, half overgrown with marsh-loving weeds, whose roots feed in the sloppy water which overlies the pitch.  But, as yet, there was no sign of the lake.  The incline, though gentle, shuts off the view of what is beyond.  This last lip of the lake has surely overflowed, and is overflowing still, though very slowly.  Its furrows all curve downward; and it is, in fact, as one of our party said, ‘a black glacier.’  The pitch, expanding under the burning sun of day, must needs expand most towards the line of least resistance, that is, downhill; and when it contracts again under the coolness of night, it contracts, surely from the same cause, more downhill than it does uphill; and so each particle never returns to the spot whence it started, but rather drags the particles above it downward toward itself.  At least, so it seemed to us.  Thus may be explained the common mistake which is noticed by Messrs. Wall and Sawkins {148b} in their admirable description of the lake.

’All previous descriptions refer the bituminous matter scattered over the La Brea district, and especially that between the village and the lake, to streams which have issued at some former epoch from the lake, and extended into the sea.  This supposition is totally incorrect, as solidification would have probably ensued before it had proceeded one-tenth of the distance; and such of the asphalt as has undoubtedly escaped from the lake has not advanced more than a few yards, and always presents the curved surfaces already described, and never appears as an extended sheet.’

Agreeing with this statement as a whole, I nevertheless cannot but think it probable that a great deal of the asphalt, whether it be in large masses or in scattered veins, may be moving very slowly downhill, from the lake to the sea, by the process of expansion by day, and contraction by night; and may be likened to a caterpillar, or rather caterpillars innumerable, progressing by expanding and contracting their rings, having strength enough to crawl downhill, but not strength enough to back uphill again.