Page:Popular Science Monthly Volume 40.djvu/236

224 sands and muds, and tilted up and worn down, during the evolution of their present form. There is a quarry at Meriden where one lava-sheet may be seen lying directly upon the scoriaceous, ropy surface of an older one. Evidently, the region has witnessed volcanic action, as the ash-bed implied. Perhaps we fail to recognize the cone at the point of outburst because it has been partly worn away. There are many volcanic regions where the eruptive action is not so recent as in Auvergne, and where the cones are consequently somewhat out of repair; deep gulleys furrow their sides and destroy their symmetrical form. Something of this may, indeed, be seen in Auvergne, for the volcanoes there are not all of the same age. Some are sadly wasted, and are recognized as volcanoes only because their remnants of lava-flows and ash-beds all slope away from a central lava-mass, which marks the place of the vent. It is chiefly in this way that the Madeira Islands differ from the Azores; the latter possess many cones of regular form, but the older volcanoes on the former are deeply dissected; so much so that it is difficult to reconstruct the original cones from which the present rugged hills and ridges have been carved out. The same contrast may be seen on a grand scale in the Hawaiian Islands, as described by Dana. The most southeastern of the group is the most recent. It is the largest, and is in the best repair; not a volcanic cone of the usual steep-sided form, indeed, but of long, smooth, gentle slopes, because its lavas were too liquid when erupted to stand on steep slopes such as are formed by heaps of ashes and cinders. Other islands farther to the northwest in the same group are mere wrecks; their edges are cut off by the waves, forming great sea-cliffs, their slopes are scored by deep ravines and canons, and their once even profiles are replaced now by sharply notched outlines. Yet nothing of even those angular forms is to be found about Meriden. If the absence of the cone from which the ashes came is due to wearing away, it must truly have been worn out.

There is, however, another method of disposing of volcanoes that has been practiced in Italy. The cone has either been blown to pieces and scattered by violent eruptions, or has been allowed to sink down by the withdrawal of lava from beneath its foundations. In either case, a great basin, often holding a lake, marks the site of the lost cone. There are several lakes of this kind in Italy—Trasimeno, Bolsena, Bracciano, and others; Sumatra possesses some huge basins of the same pattern; but there are no such basins in Connecticut. There are no lakes at all near Meriden, and the lakes in the back country are only old valleys obstructed by glacial drift.

There is an account of an old volcanic region out in New Mexico that may, perhaps, guide our search. In the district of the