Page:Popular Science Monthly Volume 71.djvu/187

Rh The Lava Flow of 1869.—One of the chief difficulties in ascending Colima from the north side is the necessity of crossing the rough lava flow which was poured out from the secondary cone in 1869. The north side of this flow is very precipitous, as its highest point rises considerably above that of the central portion of the flow, thus forming a kind of wall on the north side. A more rapid cooling of the outer edge of

the molten lava stream than that of the center formed this wall. As a result the sides hardened rapidly and consequently have an altitude about equal to that of the stream at its greatest height. The central portion, remaining hot for a longer time, flowed on after the lava had ceased to flow from the cone, and thus lowered its surface. In August, 1869, a month after the principal eruption, the lava is said to have flowed a little more than nine feet per day. The surface of this lava is as scoriaceous, irregular and crumbly (aa), as one can well imagine, but does not differ greatly from the mal pais seen in other parts of Mexico. Because of this character, one is obliged to walk with the greatest care, stepping over or descending-into fissures, climbing up or over irregular masses of scoriæ. Indeed, the roughness of the lava hurts the hands and tears the shoes, and its treacherous character compels one to be on the alert at all times, which makes the work very exhausting.

Secondary Cone.—The secondary cone is composed of a compact though somewhat vesicular andesite with a steep slope. From this cone, as has been said, lava poured forth in 1869. There is no crater in the cone, although the summit is broken by three parallel fissures.