The Benthic Zone.
The Sand Skink get its water from maybe lakes, rivers, or ponds i believe.
An island or sand bar
Lakes are different from ponds because lakes are bigger than ponds and the sunlight is able to hit the bottom of a pound and create algae. The sunlight is not able to hit the bottom of a lake.
Clay and loam are both commonly placed on the bottom of ponds.
Click on the link for a picture on a different website.
Many people say in the bottom of ponds or lakes.
No
Pond weed is a weed that grows on the bottom of ponds.
A mixture of sand and water would be a heterogeneousmixture since most of the sand will settle to the bottom and only the tiniest grains will remain suspended in the water.
Flat Bottom Hull
For aesthetics it usually looks better to have a smooth bottom. In most cases it will not effect the liners fit of function. Upon new installation you may notice some inconsistency in the bottom as it's hard to install without disrupting the sand. Some of this will likely flatten out as the weight of the water acts upon the sand.