(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.
It is thickened more in some places than in others, and thus are formed the spiral, annular and other markings, as well as the pits which occur on various cells and vessels.
Pit-threads whIch traverse the closing membrane of the pits in the FIG.
Specimens of these from the Dippen Hall pits, analysed by Messrs J.
The immense volumes of sulphurous acid evolved give rise to many complaints; all the minor pits suspend work during the summer to avoid destruction of the crops.
Railways had their origin in the tramways (q.v.) or wagon-ways which at least as early as the middle of the 16th century were used in the mineral districts of England round Newcastle for the conveyance of coal from the pits to the river Tyne for shipment.
In both types pits are constructed between the rails on which the engines stand to afford easy access for the inspection and cleaning of their mechanism.
Large pits containing deposits of white sand, clay and pebbles are found in the limestone at Longcliff, Newhaven and Carsington.
Large pits are dug across the line of advance of these great insect armies to stop them when in the larval or wingless stage, and even huge bonfires are lighted to check their flight when adult.
The plain on the right of the marshes was prepared with pits and spikes.
They are found one on each cephalic tentacle, and are simply minute open pits or depressions of the epidermis, the epidermic cells lining them being pigmented and connected with nerves (compare fig.
A little later, in Crete, bone-pits seem to have come into use, containing the remains of many burials.
John Pits 1 says, but apparently without authority, that he became a Benedictine monk.
B, Section through compound eye (after Miall and Denny); C, organs of smell in cockchafer; (after Kraepelin); D, a, b, sensory pits on cercopods of golden-eye fly; c, sensory pit on palp of stone-fly (after Packard); E, sensory hair (after Miall and Denny); F, ear of long-horned grasshopper; a, Front shin showing outer opening and air-tube; b, section (after Graber); G, ear of locust from within (after Graber).
The pits leading from these lengthen into tubes, and undergo repeated branching as development proceeds.
Herodotus describes the oil pits near Ardericca (near Babylon), and the pitch spring of Zacynthus (Zante), whilst Strabo, Dioscorides and Pliny mention the use of the oil of Agrigentum, in Sicily, for illumination, and Plutarch refers to the petroleum found near Ecbatana (Kerkuk).
Here the pits split into two, one part ending in a sac lined with sensory epithelium, and embedded in nervous tissue, the other projecting backwards as a long, glandular, blind canal.
Two lateral, shallow pits occur on the side of the body about the level of the hinder end of the proboscis in some species of the genus Carinella, which are termed side-organs.
Many other parts of the province have pits for private use.
His work, Monumenti delle anti christiane primitive, is the first in which the strange misconception, received with unquestioning faith by earlier writers, that the catacombs were exhausted sand-pits adapted by the Christians to the purpose of interment, was dispelled, and the true history of their formation demonstrated.
Valuable salt is obtained from the pits at Dolnja Tuzla, and the southern part of Herzegovina yields asphalt and lignite.
The chitinous chaetae have their origin in special ectodermal pits, at the base of which is one large cell which is thought to secrete the chaeta, as in Chaetopods.
These pits are not isolated, but are connected by an ectodermal ridge, which grows in at the margin of the mantle and forms a continuous band somewhat resembling the ectodermal primordium of vertebrate teeth.
To the west of the main shaft were three square pits with horses and their harness, and by them two pits with men's skeletons.
When the location of the deposit has been determined approximately, further search is made by trenches or pits or borings through the surface soil.
By sinking additional pits or by extending the costeaning trenches and uncovering the outcrop of the deposit more fully it is sometimes possible to obtain all the information required for the most extensive and important mining operations.
For deep workings the milling method is usually employed, in which the ore is excavated in funnel-shaped pits, each of which connects with underground haulage roads by a shaft.
Before the bottom of these pits reaches the level of the haulage roads below, a new set of roads will have been driven at a lower level and connected with the excavations above by the shafts.
No shelter had been provided for the inmates: the first arrivals made rude sheds from the debris of the stockade; the others made tents of blankets and other available pieces of cloth, or dug pits in the ground.
In the United States and Scotland rectangular pits secured by timber framings are still common, but the tendency the pressure being reduced to that of the external atmosphere when it is desired to open the upper door, and increased to that of the working space below when it is intended to communicate with the sinkers, or to raise the stuff broken in the bottom.
Long, also lined with amalgamated copper plates, after the pyritic and other heavy minerals have been separated by depositing in catch pits and other similar contrivances.
The lining of these pits is amply supplied with branches from the trigeminal nerves, but the f unction is still quite unknown.
In 1904 a few trial pits were sunk by M.
In practice the proximity to chalk pits or lime kilns, the cost of the lime and cartage, will determine which is most economical.
On the stiff soils overl y ing the chalk it was formerly the custom to dig pits through the soil to the rock below.
The material is dug from neighbouring pits or sometimes from the fields which are to be improved, and applied in autumn and winter.
The clay is dug from the land or from ditches or pits and placed in heaps of 60 to ioo loads each, with faggot wood, refuse coals or other fuel.
Stomata are often situated at the bottom of pits in the surface of the leaf.
Simple pits (p.) enable conduction to take place readily from one to another.
Note thick walls and oblique slit-like pits with opposite inclination on the two sides of the cell seen in surface view.