no water can be expected in the dry season. Mr. Speyer had taken the first road; our company preferred the second, because we had but four small wagons along, and we would gain from 20 to 30 miles travelling by it. From want of water we had nothing to fear, as the rainy season had commenced, and daily showers provided us with a greater abundance of it than we liked.
On the first day we started rather late from Paso, but yet made 24 miles without rest. To our right was a mountain chain running, probably of limestone: to our left, the receding valley of the Rio del Norte, which takes here a southeastern direction, and from which a high chain of mountains will soon separate us entirely. Our road passed over a wide sandy plain, covered with mezquite, and similar shrubbery. It was strewn with two kinds of limestone; the one of the same character as I had seen in Paso, and the other of a chalk-like appearance, probably a fresh-water limestone. Pieces of the first were frequently enveloped by a white crust of the latter. We camped near the road in the plain, with tolerable grass and plenty of rain-water.
August 16.–Travelled this morning but eight miles, and halted, with good grass and rain-water. Ahead of us were the much-dreaded sand hills, (los médanos,) an immense field of steep sand ridges, without shrub or vegetation of any kind, looking like a piece of Arabian desert transplanted into this plain, or like the bottom of the sea uplifted from the deep. Several springs, I am told, are found near the sand hills; and it is not at all unlikely that this whole ground was once covered by a lake. One spring in particular, forming a water-hole at the foot of the sand hills, and called ojo de malayuque, is known as a usual camping place on our road, but we stopped before reaching it. Though we shall pass but the lowest depression of the hills, near their western limit, it will nevertheless be a hard day's work, and we prepared our animals for it by a long rest.
About noon, while we were encamped, a thunder-storm came on, as usual in the rainy season. It rained awhile, and towards the end of the shower, the thunder disappearing in the distance, I perceived a most remarkable phenomenon in the mountains to our right, about 10 miles distant. Three pointed flames, apparently from one to two feet high, and of whitish lustre, were seen at once on a high barren place in the mountains; they lasted for about 10 minutes, and disappeared then as suddenly. The Mexicans told me that this phenomenon is not uncommon in these mountains, and that such a place had once been examined, and a crevice found, around which the grass was burnt. The popular opinion amongst the Mexicans seems to be, that such flames indicate silver mines. There can be hardly any doubt that the phenomenon is connected with electricity; but whether an inflammable gas, that emanates from a crevice, is ignited by lightning, or an unusual quantity of free electricity is developed by local causes, or superficial metallic layers should have some influence in producing it, are questions that can only be solved by a repeated and careful examination of the localities and circumstances. In the afternoon we commenced our march for the sand hills. For six miles we had to travel over a sandy and hilly country, before we reached the sand hills proper, which are here six miles wide. On the first part of the road I saw rocks of a reddish brown porphyry, encrusted sometimes with chalk-like limestone, but no more pieces of limestone. The form of the mountains, too, on our right,
