638 PROCEEDINGS OF SECTION J. 



brickwork packed solid to the rock with sandstone concrete. 

 In very wet rock a ring of brickwork (four and a-half inches) is 

 laid inside an outer lining of concrete and sub-ducts, which were 

 afterwards closed, were used during construction in order to secure 

 water-tight work. The outfall sewer from Oxford-street to the 

 ocean, a length of four and a-quarter miles, is rendered to three- 

 fourths of its height, and the brick arch above that level is 

 pointed. The remainder of the outfall sewer and the branch 

 sewers are rendered all round with cement mortar, composed of 

 one part Portland cement and two parts of sand. Every lot of 

 cement brought on the work is tested at the head office, where 

 complete testing apparatus is provided, and all cement which does 

 not fullil the specified conditions, or appears to be of inferior or 

 doubtful quality, is rejected. The sewers are constructed chiefly 

 in tunnels, and a great portion of the tunnelling is in sandstone 

 I'ock. Numerous shafts were sunk for the driving of the tunnels, 

 and to be used for ventilation afterwards, the deepest one being 

 two hundred and forty feet. The rock tunnel excavation was 

 done by blasting, and presented no difficulties. In some cases the 

 drilling was done by percussive rock drills worked by compressed 

 air, and where compressed air was used for this purpose it was 

 also used to work the winding engines. In other cases the drilling 

 was done by hand, and ventilation was provided by Root's blowers. 

 The outfall end of the sewer for a length of about four miles lies 

 in more or less open country, and the blasting operations cause 

 little or no inconvenience : but, having regard to the annoyance 

 and inconvenience to the citizens, which must result from blasting 

 operations within the city, inquiries were made as to the prac- 

 ticability of getting a rock-boring machine which would reduce to 

 a minimum, or, if possible, altogether do away with, the necessity 

 for blasting. In 1845 the first machine of this kind was invented 

 for use in the Mont Oenis tunnel, but it was not perfected till 

 1849, and in the following year it was abandoned as being im- 

 practicable. Since that time many tunnel-boring machines have 

 been invented and patented in England and America. Some 

 were designed for cutting an angular groove round the periphery 

 of the tunnel, and others were designed for making a cylindrical 

 bore of the whole area. A machine of the former type was tried 

 on the first section of the outfall sewers constructed, but it proved 

 impracticable. One of the most promising of the latter type is 

 the machine known as Brunton's, in which the boring is done by 

 revolving cutters, and one of these machines to make a circular 

 bore of seven feet diameter was specially made in London for this 

 work, and imported, and it had a lengthened trial, extending over 

 a period of about six months, during which time a length of sixty- 

 six feet was bored, being at the rate of one mile of tunnel in forty 

 years. The use of the machine was then abandoned, and the 

 work proceeded in the ordinary way. The cause of the failure 



