52 NINTH REPORT. 



No one of these earthquakes was of catastrophic violence, but we should not 

 on this account tlelude ourselves by any false hopes that this condition will 

 continue. The so-called "Charleston" earthc[uake came as a complete sur- 

 prise, perhaps even to many ocologists, but data were in existence ujion lhe 

 basis of which it might have been predicted, though without even a guess as 

 to the time of its arrival. The devastating earthcjuake which will sometime 

 visit the cities upon the fall line, may not befall in our generation or that of 

 our children or grandchildren, but come it will eventually. When the blow 

 has fallen the cities will be safer because they will know their danger and 

 may, perhaps, rebuild with some reference to it. Despite their disastrous 

 consequences earthquakes have served a useful pu'rfiose by revealing the 

 lines of special movement where they pass beneath the cities, and as soon as 

 possible after the shocks have passed, a detailed map should be prepared set- 

 ting forth the distribution of their intensity within each city upon the basis 

 of the damage sustained by its artificial structures. Over the positions of 

 greatest damage public ])arks, or wide streets should he laid out in the re- 

 building of the city, and on no account should structures be again reared 

 above them. To proceed in an}^ other manner is to court destruction. 



To one who has followed me in this address, I think it is not necessary to 

 say that, in my view, earthquakes result from nuitual adjustments of the 

 blocks which compose the earth's crust and are outlined by a system of 

 fractures. Such fractures, large and small, w^e have seen are actually in 

 view at the surface after any great earthquake and may be counted by the 

 hundreds, or even thousands. A still larger number, upon which the ampli- 

 tude of the movement has ])resumably been less, do not a]:)pear at the surface 

 as fractures, though their course is marked out by the lines of special destruc- 

 tion. 



It is not necessary to assume that these fractures have originated through 

 the action of those forces which engendered the earthf[uake; indeed, it is far 

 more likely that most of them existed before, and that the earthquake is the 

 consecjuence of displacements which have occurred upon them. We have 

 only to look about us in those places where ledges of rock are exposed at the 

 surface to note that when undisturbed from their original position these 

 rocks are everywhere intersected by a network of fissures generlly perpen- 

 dicular to the earth's surface and arranged in a number of intersecting but 

 jDarallel series. By these fissures the rock}^ crust is divided into an immense 

 number of vertical prismatic blocks, which grouped together, make up masses 

 of any size or outline whatever, though ahvays bounded by a vertical wall 

 and capable of being moved en bloc upward or downward, laterally past each 

 other, or, even when crushed to some extent, tilted from their position of 

 horizontality. Such movements are the ones actually indicated upon the 

 earthquake faults which are open to our inspection. 



T shall not consider myself called upon to give here the reasons which have 

 led geologists in recent years to regard the outermost portion of the earth's 

 crust in which are the fractures above described, as resting, and potentially 

 lioated upon a lower rock zone within which a flow of material is the only wa>- 

 in which adjustments may occur. It is enough to say that the view is based 

 upon a consideration of gravitation and the strength of rock material, and 

 confirmation for it is found in the observed behavior of the earth's surface. 



It is a fact Avell known that while some seacoasts, like those of Maine and 

 Norway, have been sinking, others, like that of Florida, have been rising. 

 Upon the continents mountain ranges continue to push up their heads, 

 while the tireless forces of erosion and transportation are as steadily planing 



