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ascent of subterranean water at the junction between the “sedimentary and the 
metamorphic formations,’’? as he found them numerous in the neighborhood of © 
the junction line. We, however, observed no such relation, and give below our 
explanation of their formation. 
Claypans vary in diameter from a few feet up to as much as three-quarters 
of a mile, a common size being from 40yds. to 100vds. They are exceedingly 
shallow; the depth of the bottom below the general level of the surrounding 
sandhills or plains is seldom greater than 5ft., and usually much less, being in 
the majority of cases not more than 2ft. to 3ft. In some cases the edge of the 
depression is ill-defined, the plain merging almost imperceptibly into the clay- 
"pan, and the only indication of the circumferential limits is the ring marking 
the edge of the deposit of fine silt which covers the bottom and sides of the 
claypan. Jn other cases the sandhills come to the very edge, and form a 
well-defined rim to it. The area drained by them is limited to a very narrow 
peripheral belt. As a general rule water does not remain in them very long; 
some of the best hold water for three or four months, but in the great majority 
of cases, especially of the smaller ones, the water disappears from them at the 
end cf a month or two. There are exceptional instances, however, of which 
Conlon Lagoon is an example, in which water would remain for very much 
longer periods. 
The water of the claypans has generally a reddish-yellow color, due to the 
presence of a quantity of very fine mud of that color held in suspension, which 
on evaporation of the water is deposited on the bottom of the claypan as a fine 
silt with a peculiar glazed surface, due perhaps to the extreme fineness of the 
last portion of the sediment deposited. On drying, this mud loses water and 
splits in all directions, cracks as much as a quarter to haif an inch wide making 
their appearance and separating the more or less rectangular masses from each 
other. 
The following explanation of the method of their formation has suggested 
itself to us. They naturally occur only where the country is flat, 7.¢., where 
the slope of the ground is not decided enough in any particular direction to 
cause the surface water to flow in that direction. There is therefore a tendency 
for the water to lie on the surface, or rather to be gathered into slight de- 
pressions, which are sure to exist even on otherwise almost level surfaces. At 
first the water that was gathered into these slight depressions would almost 
immediately percolate the porous strata, but in doing so it would leave behind a 
deposit of silt. This would happen with every subsequent heavy fall of rain, 
until the silt suspended in the water and carried into the depression and de- 
posited there was in sufficient quantity to prevent further percolation. 
The claypan has now become established and will retain water for a longer 
or shorter period, and as there is now very little percolation through the bottom 
there will be no further settling of the floor as there may have been in the early 
stages. The depth of the claypan in many cases will, however, be increased by 
the growth of the rim by the deposition at the water’s edge of the fine particles 
of sand, &c., driven along the surface of the ground by the wind. In this 
manner the rim may be added to from time to time, and the holding capacity of 
the claypan thereby increased. 
The largest example of a claypan seen during the expedition is one that 
occurs a few miles to the south of Heavitree Gap, and known locally as Conlon 
Lagoon. In its greatest dimensions it is a quarter of a mile wide and three- 
