Bottom compositions are notated on charts using a system of letters that convey the necessary knowledge to the navigator. At first, these markings may seem random and confusing, but when you boil the system down to it's basics it turns out to be rather intuitive.
Chart symbols referring to the bottom composition will be located amongst depth soundings and will begin with a capital letter. If the symbol is only one letter, then it will be capital. Modifiers about the bottom composition will be in lower case letters.
R, Rk: Rock
Bo, Blds: Boulders
Co Hd: Coral Head
Vol Ash: Volcanic Ash
Modifiers to the bottom composition are:
Once you know the language, it is simply a matter of putting the words together to spell out the bottom conditions. They are always stated with the main bottom constituent first.
fS M bk Sh: Fine Sand with Mud and Broken Shells
S/M: Two layers, Sand over Mud
hS Sh: Hard Sand with Shells
Just remember that modifiers about the bottom are in lower case letters, while the bottom composition starts with a capital letter. When the bottom is composed of more than one substrate, it will be listed from main bottom constituent, followed by the lesser constituents.