1890.] Geology and Paleontology. 947 
On the south coast of Kauai, in the district of Mana, sand-dunes 
attaining a height of over one hundred feet extend a mile or more 
nearly parallel to the sea, and covering hundreds of acres with the 
water-worn and wind-blown fragments of shells and coral. The dunes 
are terminated on the west by bold cliffs (Pali), whose base is washed 
by the sea ; at the east end the range terminates in a dune more sym- 
metrical in shape than the majority, having on the land side the 
appearance of a broadened, truncated cone. The sands on the top 
and on the landward slope of this dune (being about 100 yards from 
the sea) possess remarkable acoustic properties, likened to the bark of 
adog. The dune has a maximum height of 108 feet, but the slope of 
sonorous sand is only sixty feet above the level field on which it is en- 
croaching. At its steepest part, the angle being quite uniformly 31°, 
the sand has a notable mobility when perfectly dry, and on disturbing 
its equilibrium it rolls in wavelets down the incline, emitting at the 
same time a deep base note of a tremulous character. My companion 
thought the sound resembled the hum of a buzz-saw in a planing-mill. 
A vibration is sometimes perceived in the hands or feet of the person 
moving the sand. The magnitude of the sound is dependent on the 
quantity of sand moved, and probably to a certain extent upon the 
temperature. The drier the sand, the greater the amount possessing 
mobility, and the louder the sound. At the time of my visit the sand 
was dry to the depth of four or five inches; its temperature three 
inches beneath the surface was 87° Fahrenheit, that of the air being 
83° in the shade (4.30 P.M.). 
When a large mass of sand was moved downward I heard the sound 
at a distance of 105 feet from the base, a light wind blowing at right 
. angles to the direction. On one occasion horses standing close to the 
base were disturbed by the rumbling sound. When the sand is clapped 
between the hands a slight, hoot-like sound is heard ; but a louder 
sound is produced by confining it in a bag, dividing the contents into 
two parts, and bringing them together violently. This I had found to 
be the best way of testing seashore sand as to its sonorousness. The 
sand on the top of the dune is wind-furrowed, and generally coarser 
than that of the slope of 31°, but this also yielded a sound of unmis- 
takable character when so tested. A bag full of sand will preserve its 
power for some time, especially if not too frequently manipulated. 
creeping vine with a blue or purple blossom (kolo-kolo) thrives on 
these dunes, and interrupts the sounding slope. I found the main slope 
120 feet long at its base, but the places not covered by this vine gave 
