The text from the [diagram of Geological Systems] giving the Names of Systems, and Characters of Rocks is reproduced here, the thickness of each division, measured from the diagram, is given as a percentage:
TERTIARY
- Recent & Pleistocene {1%} sands, superficial deposits
- Pliocene {1%} sands, superficial deposits
- Eocene {4%} clays and sands chiefly
SECONDARY
- Cretaceous {6%} chalk at top
sandstones, mud and clays below - Jurassic {7%} shales, sandstones and oolitic limestones
- Triassic {5%} red sandstones and marls, gypsum and salt
PRIMARY
- Permian {3%} red sandstones & magnesian limestone
- Carboniferous {16%} sandstones, shales and coals at top
sandstones in middle
limestone and shales below - Devonian {8%} red sandstones, shales, slates and limestones
- Silurian {9%} sandstones and shales, thin limestones
- Ordovician {11%} slates, shales, sandstones and thin limestones
- Cambrian {14%} slates and sandstones
- Pre-Cambrian {15%} sandstones, shales and volcanic rocks