PICKERING. — LUNAR AND HAWAIIAN PHYSICAL KEATUKES COMPARED. 153 
that a large engulfment crater formerly existed upon Kauai, and another in southern 
Hawaii, near the coast, south of Mauna Loa, hut the writer w s unable to examine 
either of these regions during his recent visit. The latter crater must have been 
about five miles in diameter, the former perhaps much larger. The largest engulf- 
ment crater known is Crater Lake, Oregon, measuring five by six miles in diameter, 
with a depth of about 3,000 feet. Next to it comes Haleakala in the Island of 
Maui, Hawaii, measuring seven miles in length by two in width. It is about 2,000 
feet deep. 
The secondary craters found upon the lunar maria are so small that it is impos- 
sible to study their interiors to advantage; we shall therefore content ourselves 
with comparing the Hawaiian formations, as far as possible with the large pri- 
mary formations of the Moon, without regard to the great discrepancy in thcii 
relative size. 
On the Hawaiian Islands with the exception of the three great craters of 
Haleakala, Mokuaweoweo, and Kilauea, few of the crater pits exceed half a mile in 
diameter, measured on their crater floors, or former free liquid lava surfaces, although 
there are probably several hundred pits over 200 feet in diameter. In addition to 
these are countless cinder cones, spiracles, etc. On the Earth at present the cooling 
process always intervenes before great size is attained. Doubtless formerly the lava 
was hotter when it first issued from the interior than it is now, also the solid crust 
resting on the liquid mass was thinner, so that the channel communicating with the 
interior was shorter and of greater diameter, thus offering a freer passage to the 
liquid flow. 
Terrestrial craters may be divided into three classes, according to the materials of 
which they are composed. These are (a) tuff or tufa cones, which are made of 
hardened volcanic mud, (b) cinder cones, made of scoria, lapilli, or sand, that is, lava 
broken up into masses of varying size, by the action of steam, from stones several 
inches or even feet in diameter to fine powder, and (c) lava craters, where the lava 
occurs in unbroken masses. It is this third class, where less water is involved in the 
eruption, which most resembles what we find upon the Moon. Representatives of all 
three classes are to be found in Hawaii. Many volcanoes like Vesuvius eject both 
cinders and lava. 
The third class may again be divided into four subdivisions according to the shape 
of the craters, namely : lava cones, lava pits, lava rings, and lava bowls. Although 
sometimes of small size, the lava cones often emit vast volumes of lava, which taking 
the form of broad streams may extend for many miles. The lava pits are by far the 
