National Geographic : 1919 Apr
IN THE COURSE OF THE CENTURIES THE STREAMS OF WATER WHICH WERE ABLE TO FORCE THEMSELVES UP, EVEN THROUGH THE THICK BED OF LAVA, HAVE HOLLOWED OUT CANYONS OF GREAT DEPTH AND WIDTH :ASCENE NEAR UDJ ASSARU Such a canyon is seen here; one also sees that the mass of pumice was not worn away evenlyand equally at allspots bythesolvent action of the flowing water. In places the stone offered a sturdier resistance to the abrasive influences,and the result was the formation oftens of thousands of cones, some of which are free-standing, while others are closely engaged with each other. Inthis picture weseeone side ofa valley formed by erosion. On the left the rim of the bluff gives approximately the original levelofthe pumice-field. Inthe center isasmall, but perfect cone. In the middle distance there is stratification, which runs through cones and obelisks that arenow entirely free-standing; where stratification appears, the cones are more in the shape of obelisks, such as are illustrated on page 295.