220 COALFIELDS AND COLLIERIES OF AUSTRALIA. 



have flat faces and peculiarly undercut sides, the width of the 

 face and the base of the thread being one half the pitch. The 

 pump cylinder fits the perimeters of the thread, space enough 

 being left between the screws and the cylinder and between 

 the faces of the iiiterrneshing threads to allow a close-running 

 fit without actual contact. There is no end thrust of the 

 screws in their bearings, because the back pressure of the 

 column of liquid is delivered to the middle of the cylinder, 

 and the endwise pressure upon the screws in one direction is 

 exactly counterbalanced by a like pressure in the opposite 

 direction . The suction connection opens into a chamber under- 

 neath the pump cylinders. The water passes- through the 

 chamber to the two ends of the cylinder, and is forced from 

 there to the centre by the two pairs of intermeshing threads, 

 the discharge being in the middle of the top of tlie cylinder 

 (D). The power to drive the pump is applied to one of the 

 shafts, the second shaft being driven by means of a pair of 

 gears (G). Having no valves, no internal packing, and no 

 small moving parts, the pump is not very liable to get out of 

 order, and as the screws are not in contact with the cylinders 

 or with each other, the consequent absence of wearing sur- 

 faces gives the pump great durability. The rotary motion 

 of all the moving parts and the continuous flow of watejr does 

 away with the churning effect produced by reciprocating 

 pumps. 



The locomotive shed and workshops are erected on the 

 flat opposite the company's coke works, which are at present 

 leased to Messrs. Figtree. There are 42 beehive ovens in this 

 plant. 



The Osborne-Wallsend Colliery. 



This colliery, commonly known as Mount Keira Colliery, 

 is situated near AV T ollongong ; it has been managed by Mr. j. 

 C. Jones for the past six years on behalf of Messrs. E. Vickery 

 and Sons, Ltd., the under-manager being Mr. Bissell. This 

 is the oldest colliery on the South Coast, having started opera- 

 tions fifty or sixty years ago. 



There are three tunnels penetrating the mountain, all of 

 which are intakes. One is the main haulage tunnel, another 

 is the travelling road, while the third is only used for ventila- 

 tion purposes. The stentons connecting two tunnels, when 

 no longer required, are generally stopped with four and a half 

 inch brickwork, which is found sufficient if the roof is not too 

 heavy; but the wall is made thicker at the sides where the coal 

 is not so strong. An air shaft three hundred feet deep sunk 

 from the top of the mountain, is situated about two miles 

 N.W. from the entrance of the main tunnel; this serves as an 

 upcast, the air being sucked out by a 12ft. Walker fan. This 

 fan is driven by three ropes from an engine. There is a pair of 



