89 



be localK' iina\ailal)k' ; or the knowledge lo he gained from e.\[)erinienting willi otlier 

 woods might be the controlling factor. But aside from such exceptional cases, it may 

 be laid down as a general rule that a timber can have no practical value for piling 

 purposes unless it is available in sufficient (luantities for general use and at a cost 

 commensurate with the service to be secured from it. 



Records show that improtcctcd timber piling of the original San Francisco 

 wharves was destroyed in from .^ to .^ \ears and was probably unserviceable after 

 3 years. This same condition prevails toda\-, with nian\- instances of complete de- 

 struction in a single season. 



Destruction is most rapid near the Golden Gate. Elsewhere in the Bay longer 

 life may be secured because of local conditions. That the results to be obtained with 

 untreated piles are directly governed In- their exposure is illustrated by the experience 

 of the San Francisco-Oakland Terminal Railways (now the Key System Transit Co.). 

 In 1902 this company built a long trestle of unprotected timber extending into the 

 Bay from the Oakland shore. No other structures existed to the north except a few- 

 small minor wharves, and the nearest to the south was Oakland Long Wharf, about a 

 mile away, built of creosoted piling and practically free of borers. The structure was 

 unmolested for about five years. Not long after that the borers were found to he at 

 work, and their attacks continued with increasing severity until in 1913 thirty- un- 

 protected timber anchor piles were destroyed in a single season. Since that time it 

 has been necessary to use treated piling in the structure. 



This would seem to indicate that an untreated pile structure in a location isolated 

 from structures known to be harboring marine pests can he expected to last consider- 

 ably longer than an untreated pile structure in close proximity to structures known to 

 be infested. This is true in spite of the fact that the marine pests are present at all 

 times. Untreated piles are also more severely attacked at the outer end of piers, or in 

 deep water, than they are inshore or in shallower water. Unusual local conditions may 

 affect the attack, as shown by the experience of the Howard Go. with gas plant wastes 

 discharged nearby, discussed on p. 57. 



Redwood, Port Orpord Ced.\r, Western Red Ced.vr 



These closely allied woods have been and still are frequently asserted to be im- 

 mune to marine borers. They are not. There is some evidence tending to show rather 

 greater resistance than in some other woods; but the e\'idence is often conflicting. 

 These woods are not as strong as Douglas fir for general piling use. They are not in- 

 frequently used, however — especially redwood in this region — in collateral or special 

 construction exposed tt) marine conditions. In one case redwood conduit pipe carrying 

 into the hay water which had a temperature of over 135° F. was not only attacked by 

 teredo but the pests were able tf) follow this pipe for over a thousand feet and destroy 

 the redwood tank with wliich it connected, far from tidewater, so severely as to make 

 necessary its practical replacement. 



Cottonwood 



Cottonwood piling has been widely reported to ha\'e given very long life in wharves 

 in Alaska, the lite thus far secured being reported in two cases as 10 and 28 years and 

 the water known to be thoroughly infested by marine borers. There are no available 

 data establishing the exact species of timber used there, and the inference that it may 

 have been some other timber, or that the data themsehes were in error, is suggested by 

 the quite opposite results secured in experiments made by the Chicago, Milwaukee & 

 St. Paul and Northern Pacific railroads at Seattle and h\- the -Southern Pacific Co. at 



