G. H. HALLIGAN. LXXIIL 



nature very seriously retards the progress of boring, and it is 

 mainly this defect which prevents the diamond drill being used 

 more extensively for many purposes for which it is otherwise so 

 admirably suited on account of the solid core which it brings up. 

 Another objection to the use of the diamond drill, in many in- 

 stances, is the necessity for providing an absolutely rigid staging 

 from which to work, and a solid foundation for the engine work- 

 ing the rotating tool. When work has to be done afloat this 

 objection is, of course, insuperable, and numerous devices have 

 been tried to enable holes to be sunk from a moving stage 

 or punt. Much ingenuity and ability have been expended in 

 perfecting the methods of boring to great depths, on shore, by 

 the many processes now in vogue, and the number of improvements 

 continually being made in the machinery and apparatus used, is 

 perhaps, the strongest evidence of its imperfection even now. 

 So far as the author is aware, nothing has been written on the 

 not less important subject of boring in deep water, but though 

 the means are not new, yet the results obtained are, in some re- 

 spects, unique. 



Advantage has been taken of the experience of others in 

 selecting the tools most suitable for the work to be done, but it 

 has been found that special circumstances called for special tools, 

 experience being the best guide in matters of this sort. 



The apparatus now in use by the Department was originally 

 designed to ascertain the nature of the bottom of the Harbour 

 down to about 40 feet below low water ; but as circumstances 

 arose necessitating an extension of this depth for bridge founda- 

 tions the gear has been gradually improved and added to, and 

 the present outfit is capable of boring through any material not 

 harder than the Hawkesbury sandstone to a depth of at least 

 600 feet. In designing the gear at present in use it was neces- 

 sary to keep in view the fact that no very extensive boring work 

 is done in any one locality, so that the portability of the 

 apparatus is of serious moment. The length of time occupied in 

 putting together the material required to sink a few holes in 

 distant parts of the country is also important, as affecting the 



