27 



enc'ccl bufurL' in lliu ri'j;i(in. In thu liny proper ihv prt-si-nce (jt borers is soon cliscKjsud 

 by Limnoria attack on tin- pile surface; but in tlu- ujiiier region the salinity is too 

 low for that borer and since the teredo attacks tiie interior of piling, without \isibly 

 affecting the exterior surface, the exposed timber showed no outward signs of a serious 

 condition. 



While the rainfall was somewhat higher in 1018, the infestation remained and 

 s[)read to all parts of the region. This prepared conditions for the great destruction 

 of whar\'es in lOlO. In that \'ear the rainfall was less than it had been ff)r o\'er forty 

 years; it has been estimated that the river discharge was less than it had lieen since 

 1863. It is likely that all the whar\'es had l:)een weakened by the attacks of the two 

 pre\ious years, and the in\asion ol I'M') completed the destruction. In the fall months 

 of that year, at the close of the breeding and settling season, whar^•es began to col- 



Fig. 13. Untreated Douglas fir piling in Oakland Estuary, destroyed by Limnoria. Good piles 

 shown are replacements. (Moore Shipbuilding Co. Photo.) 



lapse, and this continued throughout the following year. Impact of ships which 

 would ordinarily be resisted by flexure of the piling, now caused the latter to break 

 off in large groups; vibration from various impact loads produced the same result; 

 in some cases the wharves collapsed of their own dead weight. The destruction affected 

 about fifty structures with a damage estimated at 815,000,000. 



This led to the organization of the San Francisco Bay Marine Piling Committee, 

 as has already been related. The epidemic destruction continued practically as long 

 as the supply of untreated wooden pile structures lasted, until, by the end of the year 

 1921 the bulk of structures with untreated piling had been destroyed, and the damage 

 thus caused amounted in money value to at least $25,000,000. 



Destruction from marine borers in San Francisco Bay has been most active in 

 the regions nearest the Golden Gate, where unprotected timber is destroyed within a 



