1887.] 413 [Shaler. 



a sudden interruption in the organic life. The phenomena, as ex- 

 hibited in the sections, would be exactly explained by any causes 

 competent to destroy by one stroke the life over a wide field of 

 sea. On such destructions taking place, the clay element would 

 continue to be deposited though free from any admixture of lime. 

 When, after a time, organic species found their way back to the field 

 and gradually repossessed it, the limy element would be reintro- 

 duced into the strata. Postponing for the time our consideration 

 as to the source of this clay element, we will proceed to consider 

 the causes competent to bring about the sudden destruction of ani- 

 mals which lived on the sea floor over a wide field of that area. 



We know as yet little of the causes which are competent to pro- 

 duce sudden destruction of organic life on the sea floor. We may, 

 however, by a careful consideration of the known facts logically 

 arrive at certain conclusions which appear to me to be impor- 

 tant. In the first place we perceive that these destructions which 

 bring about the termination upwardly of a limestone layer come 

 suddenly over a wide field and that they affect a great number of 

 the species living on the floor. We may, therefore, assume that 

 this death is caused not by any disease affecting the creatures, but 

 by some external physical accident. It seems to me that such an 

 accident is explained by earthquake shocks. In the first place it 

 is manifest that earthquake shocks affect the sea floor with some- 

 thing like the frequency and intensity of those which operate on 

 the land. This is shown by the waves in the sea water which are 

 produced by such commotions. The amplitude of the wave itself 

 clearly indicates that the range of movement in the disturbance is 

 often as great as is ever observed on the surface of the land. At 

 their origin the waves which have repeatedly swept in upon the 

 coast of South America cannot have an altitude of less than three 

 feet and at times the movement may have amounted to as much 

 as five feet. Within the limits of human history we have known 

 of some scores of these accidents affecting the different portions 

 of the ocean basins. They do not appear to occur in the North 

 Atlantic, but the greater part of the shores of the other great 

 water areas have felt their impulse. 



The effect of a movement on the sea floor having an amplitude 

 of a foot or more would probably be disastrous to the greater part 

 of the organisms which inhabit the bottom. The rate of vibra- 

 tion of the water and the subjacent earth would be diverse. The 



