966 



SCIENCE. 



[N. S. Vol. XXIII. No. 600. 



Gonzales, so far as our reports at present 

 show, the bottom lands were more severely 

 ruptured, fissured and otherwise deformed 

 than in any other portion of the state. 

 The Spreckels Sugar Mill, situated on the 

 banks of the river, suffered more severely 

 probably than any other steel structure in 

 the state. Santa Cruz, on the other hand, 

 which is on the same side of the rift, and 

 at4he same distance from it, but which is 

 built on rock for the most part, suffered 

 much less damage. In the northern 

 counties along the coast the most severe 

 effects were felt at Ferndale, on the south 

 margin of the flood plain of the Eel River, 

 and at Petrolia, on the bottom land of the 

 Mattole. Fort Bragg was severely shaken 

 with very destructive effects, but our re- 

 ports do not yet indicate the character of 

 the ground upon which it is situated. 



In the facts which have been cited we 

 seem to have warrant for a generalization 

 as to the excessively destructive effect of 

 the earth wave as transmitted by the little 

 coherent formations of the valley bottoms. 

 But it must be borne in mind that by far 

 the greater number of structures subject to 

 destructive shock are situated in the valley 

 lands and that there has not yet been time 

 for a detailed comparison of the effects in 

 the valleys with those in the hills, where 

 the buildings are founded on firm rock 

 except in a few notable instances. 



The most instructive of these instances is 

 the city of San Francisco, and the facts ob- 

 served there are entirely in harmony with 

 the generalization above outlined. In the 

 city of San Francisco we may recognize for 

 preliminary purposes four types of ground : 

 (1) The rocky hill slopes; (2) the valleys 

 between the spurs of the hills which have 

 been filled in slowly by natural processes; 

 (3) the sand dunes; (4) the artificially 

 filled land on the fringe of the city. 

 Throughout the city we have a graded 

 scale of intensity of destructive effects' 



which corresponds closely to this classifica- 

 tion of the ground. The most violent de- 

 struction of buildings, as everybody knows, 

 was on the made ground. This ground 

 seems to have behaved during the earth- 

 quake very much in the same way as jelly 

 in a bowl, or as a semi-liquid material in 

 a tank. The earth waves which pass 

 through the highly elastic rocks swiftly 

 with a small amplitude seem in this ma- 

 terial to have been transfonned into slow 

 undulations of great amplitude which were 

 excessively destructive. The filled in ma- 

 terial and the swampy foundation upon 

 which it rests behaved, in other words, as 

 a mass superimposed upon the earth's sur- 

 face, rather than as a part of the elastic 

 crust itself. In a less degree the same 

 thing is true of the sand dune areas, where 

 the ground Avas frequently deformed and 

 fissured. In still less degree the naturally 

 filled valleys between the hill spurs were 

 susceptible to this kind of movement, and 

 the destruction of buildings was corre- 

 spondingly less, but still severe, depending 

 very largely on the character of the build- 

 ings, the integrity of their construction, etc. 

 In portions of these valleys, however, the 

 original surface of the ground has been 

 modified by grading and filling, and on the 

 filled areas the destruction was more thor- 

 ough than elsewhere in the same valley 

 tracts. On the rocky slopes and ridge tops, 

 where, for the most part, the vibration 

 communicated to buildings was that of the 

 elastic underlying rocks, the destruction 

 was at a minimum. On some of the hills 

 chimneys fell very generally and walls were 

 cracked ; on others even the chimneys with- 

 stood the shock. 



While this correlation of intensity of de- 

 structive effect appears to hold as a gen- 

 eralization, there are well known exceptions 

 which find their explanation in the strength 

 of the structures. Modern class A steel 

 structures with deep foundations appear to 



