The first petroglyph to be mentioned is found at la Cueva del Islote, on Punta Braba, about 5 leagues east from Arecibo and on the north side of the island of Puerto Rico. The grotto is found in an immense blackish mass of igneous rock, forming a point projecting into the sea, which beats furiously against it; it communicates with the sea at the foot, and the water entering this passage, which is quite narrow, produces a terrific roaring followed soon after by veritable thunder claps. The people of the neighborhood have a superstitious fear of it, and it is only with great difficulty that anyone can be found to accompany one there. The entrance on the land side is toward the east--a yawning crevasse, filled partly with rubbish and partly by the stunted vegetation of the coast. On penetrating to the interior we find, after following a short but wide passage, a pyriform chamber 20 meters in diameter. In the ceiling a very narrow crack admits a ray of light which, reflected in the water of the sea, filling the bottom of the cave, produces a bluish twilight. Notwithstanding this twilight, we are obliged to carry torches to distinguish objects. All around us, but especially over the point where the sea enters in, are to be seen the inscriptions represented here. The incisions are very deep, and the edges are generally dulled by the blows of the hammer; in certain spots, toward the lower part of the grotto, several inscriptions are partially effaced by the action of the sea, but those of the upper part are in a remarkable state of preservation. Beneath certain principal figures of the groups are little circular basin-like depressions cut in the rock with a trench running down toward the bottom.