H. H. WALES. LADO SUR DE LA ALAMEDA. CALLE DE LA ARTILLERIA No. 6. Hotel Internacional S.L.P. San Luis Potosi, de 190 Direction having a slope of 45 degrees down into the Pleistocene plain, I should estimate the grade to have a vertical depth of between 300 to 400 feet. In some shallow cuts along the Pleistocene plain I noticed outcrops of limestone shale (weathered but I think dark colored rock) somewhat disturbed by uplift. At the base of the Tertiary plain the lithology changes and a heavy bedded thick mass appears that looks to be sandstone. Above it comes in thin and heavy bedded limestones with layers having interbedded shales. The weathered surfaces of these limestones remind much of the Trenton outcrops of Kentucky. Above the limestones is a considerable thickness of soft blue greenish shales. All the strata of the Tertiary plain are tilted north dips up to 15 degrees but averaging between 5 to 10 degrees. I should think the entire Tertiary to be not less than 2800 feet in [illegible] thickness. At Las Palmas the train diverges to the left and makes for a dry stream gorge, but crossing at once of alongside the steep escarpment. When one are up about 200 feet and before one are truly in the gorge one sees over a small bridge that seemingly has no need to be here. But about 200 feet below there issues from a cave a spring—a river as large as the Little Miami near Cincinnati—which rushes away over the Pleistocene plain. The train continues to climb and soon one gains into the dry and narrow gorge, a cliff in the Tertiary scale. As one sees of these are on both sides vertical walls of the sandstone best seen at El Abra (125 Kil.) and which I photographed yesterday.