Specimens of these from the Dippen Hall pits, analysed by Messrs J.
The plain on the right of the marshes was prepared with pits and spikes.
(For the methods of boring see Boring.) The working of coal may be conducted either by means of levels or galleries driven from the outcrop in a valley, or by shafts or pits sunk from the surface.
Each strand of spiral or annular first-formed tracheids is called a protoxylem strand, as distinct from the metaxylem or rest of the xylem, which consists of thick-walled tracheids, the pits of which are often scalariform.
These fibre-tracheids are easily confused on superficial view with the true wood-fibres belonging to the parenchymatous system; but their pits are always bordered, though in the extreme type they are reduced to mere slits in the wall.