road a very large black spider, reminding me of the bird-catching spider of South America; the Mexicans consider it poisonous.
May 30.–We marched to-day through endless chaparrál 30 miles, to Mier, celebrated by the Texan invasion in 1840. It is a town with from 2,000 to 3,000 inhabitants, and has many stone buildings, while others are mere huts covered with straw. It lies on the right bank of the Alamo or Alcontre, a small river that runs, five miles below, into the Rio Grande. On the Plaza, the corner house was shown to us where the Texans, in their memorable expedition, fought against the ten-fold number of Mexicans. We encamped outside the town, near the river.
May 31.–Took a very early start this morning for Camargo, (25 miles.) Our road left here the river, but I followed its bank yet for some miles, because I had learned that some singular, large oyster-shells were found there. I had to cross many deep ravines to continue along the river, and met there with bluffs consisting of a gray limestone without fossils; but for a long while I perceived only a great number of recent shells, living yet in the river or on the shore, till I discovered at last, in a clay bank of the river, a whole bed of the supposed oyster-shells, which were in fact very large specimens of the genus Ostrea, belonging undoubtedly to the cretaceous formation. The place where I found them is close to the river, about two miles from Mier, and about three from its mouth in the Rio Grande. According to similar accounts of large oyster-shells on the upper Rio Grande, this cretaceous formation seems to extend higher up on the Rio Grande as far as Laredo, and it is most likely connected, too, with the same formation lately discovered in Texas. Loaded with specimens, I turned into the road again, and, passing several creeks, ranchos, and villages, arrived at the left bank of the Rio San Juan, opposite Camargo. The San Juan, whose headwaters we passed at Monterey, is here a broad and respectable stream that falls into the Rio Grande about nine miles below Camargo, near San Francisco. In high water, steamboats drawing five feet go from the mouth of the Rio Grande up to Camargo, and a large depot has therefore been established here by the War Department; but at present the water was too low for such craft, and we were told that we would have to march, probably, as far as Reynosa before we could find steamboats. A ferry boat, managed by a rope drawn across the river, brought us to the opposite shore, where Camargo lies. This is a town of 1,000 or at most 2,000 inhabitants at present, with some stone houses and a great many huts. The American depots and stores are generally kept in large tents or in large shanties, with wooden roofs and walls of canvass. The situation of the town, in a sandy plain, offers nothing the least attractive; but if we also add to the deep sand that covers all the streets a constant disagreeable wind, and the brackish, sulphureted water of the Rio San Juan, it must be considered a very unpleasant place.
On June 1, we left for San Francisco, (nine miles from Camargo.) I had been detained in town by some business till all the troops had left, and rode therefore alone, behind them. The road was very sandy, and the head wind filled the air so with dust and sand, that it was most painful to the eyes; on both sides of the narrow road was thick chaparrál. Riding ahead, therefore, with half-shut eyes, and reflecting upon the good chance that the guerillas would have to put an end to my scientific rambles forever, I was met by a return part of our regiment, reporting that one of our men, Mr. Swain, who stayed behind the troops, had just been killed by some
