[KLOTzl MICROSEISMS 201 



longer one of waves from a storm when a greater depth of water is in- 

 volved in the motion. 



A priori Ireasoning does not appear to furnish a conclusive reply 

 to the question whether the microseisms are attributable to the horizontal 

 or to the undulatory movements. However, the consideration of the 

 simultaneous occurrence of microseisms with certain atmospheric or 

 barometric conditions leads to the conclusion that microseisms are mostly 

 attributable to horizontal displacements. 



Having made daily comparisons with the seismograms, local baro- 

 grams and weather maps, the following conclusions have been deduced. 

 It is believed that identical atmospheric conditions prevailing over differ- 

 ent parts of the earth's surface will not necessarily produce similar 

 microseisms, as these are affected by the elasticity of the particular area 

 under consideration, also by the geological formation, the presence of 

 well-marked dykes, faults, and by the proximity of large sheets of water, 

 the ocean. One effect of the proximity of the ocean caused by barometric 

 pressure is the change of the level of the water, quite apart from the 

 tides, and this change through loading or unloading along the coast 

 produces a displacement of the pendulum zero, referred to in another 

 place. In the sea, then, we have the dual effect of the direct barometric 

 pressure and the correlated one of displacement of the water, while on 

 land we liave only the former. Barometric gradients over the* ocean 

 necessarily produce a motion of the water, quite apart from that pro- 

 duced by the winds resulting from the gradients. However the pressure 

 effect on the ocean bottom remains constant, for any displacement of 

 the water is exactly balanced by the change of atmospheric pressure. 

 Different of course it is on land which suffers the change of barometric 

 pressure. 



The feature to strike one most in the above comparisons is that 

 when marked microseisms are present we are almost certain to find in 

 the morning of the day of record for the following 24 hours an area of 

 "Low^' about the Gulf of St. Lawiience. That is, the condition of 

 " Low " in the Gulf precedes the record of marked microseisms. The 

 greater part of the Gulf is less than 150 fathoms deep. Through it runs 

 a " deep " from the mouth of the St. Lawrence ( Matane) , along the 

 south of Anticosti, passing between Cape Breton and Newfoundland 

 reaching a depth of 350 fathoms before joining the Atlantic ocean. 'This 

 deep is over the eastern part of the Great St. Lawrence and Champlain 

 Fault, shown on the Geological maps, for nearly 700 miles. The waters 

 about Nova Scotia and Newfoundland are all within the 150 fathom 

 line, so that the " Lows " over the Gulf and Sable Island are over waters 



