Geological and Miscellaneous Notice of Tarapaca. 5 



portion of resin. Parts of some of the trees have the appear- 

 ance of having been charred. From latitude 20° I have traced 

 this forest for nearly sixty miles in a southeast direction. About 

 thirty miles further north, trees have also been discovered, and it 

 appears not improbable, that the whole of this now barren plain 

 was once a fertile and thickly wooded valley. In some places 

 the branches of the trees are near the surface ; and often, receding 

 from these points in all directions, they are found more deeply 

 buried, indicating an uneven surface of the valley in which they 

 grew. 



By sinking wells through the saline soil of the pampa, water 

 has been found in some places at the depth often or twelve feet, 

 while in other parts excavations have been made eight or ten 

 times this depth without meeting with it. In general, after pass- 

 ing a few yards through marl, the wells terminate in a layer of 

 coarse sand. On the western border of the pampa are several 

 wells which have been sunk through trachyte, and brackish wa- 

 ter obtained at a depth of from twenty to thirty five feet. In 

 the neighborhood of Almonte, during my visit to that place, 

 workmen were engaged in sinking a well, and had then attained 

 the depth of one hundred and fifty feet without meeting with 

 * water. This well passed fifty feet through marl and clay, two 

 feet through coarse sand, eighty feet through clay, ten feet through 

 fine gravel, and terminated in a bed of coarse gravel and pebbles, 

 mixed with large water-worn stones. 



In the vicinity of Pica are two hot springs, one of which is 

 92° and the other 98° Fah. The water contains a small portion 

 of carbonate of soda. 



Among the hills which skirt the coast, and at their base on the 

 western side of the pampa, are beds of nitrate of soda, which 

 cover a tract of country not less than one hundred and fifty miles 

 in extent. They are slightly elevated above the level of the 

 plain, and covered by a light, dry, sandy marl, mixed with mi- 

 nute fragments of shells. This covering yields with a crack- 

 ling noise to the pressure of the feet while walking over it, and 

 thus affords an indication of the presence of nitrate of soda be- 

 neath, and is a common guide for those who are in search of it. 

 Below this, and but a few inches from the surface, there is usu- 

 ally a layer of common salt, about a foot thick, possessing a coarse 

 fibrous structure. Under this lies the nitrate of soda, resting on 



