Finally, the effects of lightning itself are sometimes such as to produce upon the mind of an impartial but unscientific beholder the firm idea that a bodily thunderbolt must necessarily have descended from heaven. In sand or rock, where lightning has struck, it often forms long hollow tubes, known to the calmly discriminating geological intelligence as fulgurites, and looking for all the world like gigantic drills such as quarrymen make for putting in a blast. They are produced, of course, by the melting of the rock under the terrific heat of the electric spark; and they grow narrower and narrower as they descend till they finally disappear. But to a casual observer, they irresistibly suggest the notion that a material weapon has struck the ground, and buried itself at the bottom of the hole. The summit of Little Ararat, that weather-beaten and many-fabled peak (where an enterprising journalist not long ago discovered the remains of Noah's Ark), has been riddled through and through by frequent lightnings, till the rock is now a mere honeycombed mass of drills and tubes, like an old target at the end of a long day's constant rifle practice. Pieces of the red trachyte from the summit, a foot long, have been brought to Europe, perforated all over with these natural bullet marks, each of them lined with black glass, due to the fusion of the rock by the passage of the spark. Specimens of such thunder-drilled rock may be seen in most geological museums. On some which Humboldt collected from a peak in Mexico, the fused slag from the wall of the tube has overflowed on to the surrounding surface, thus conclusively proving (if proof were necessary) that the holes are due to melting heat alone, and not to the passage of any solid thunderbolt.