red clay

1 :  clay that usually owes its reddish color to oxide of iron

2 :  a slowly accumulating abysmal deposit covering some 55,000,000 square miles of the deepest parts of the ocean bottom and consisting of the insoluble residual material of volcanic and meteoritic or cosmic dust mingled with nodules of manganese oxide, crystals of the zeolite phillipsite, sharks' teeth, the siliceous tests of Radiolaria, and other resistant organic debris