Cavity and solid walls. 1  A cavity wall is made up of two walls with a gap in between, known as the cavity; the outer leaf is usually made of brick, and the inner layer of brick or concrete block.  A solid wall has no cavity; each wall is a single solid wall, usually made of brick or stone.
A cladogram (from Greek clados branch and gramma character) is a diagram used in cladistics which shows relations among organisms.
Notice how the opposite sides remain parallel. A parallelogram is a quadrilateral with opposite sides parallel. But there are various tests that can be applied to see if something is a parallelogram. It is the parent of some other quadrilaterals, which are obtained by adding restrictions of various kinds: