(d) The fall of a large avalanche, or of a land-slide into the lake.

(e) And lastly, earthquakes.
Observations show that the most frequent and evident of these causes are variations of atmospheric pressure and local storms.

With regard to earthquake shocks as a cause of such fluctuations of level, it is a singular and significant fact that since Forel has established the delicate self-registering apparatus on the shores of the Lake of Geneva, no less than twelve earthquake shocks have been experienced in this portion of Switzerland, and they have had no sensible influence on these sensitive instruments.

In fact, a little consideration in relation to the character of such shocks renders it highly improbable that such brief tremors of the earth's crust could have been any agency in the generation of rhythmical oscillations of the whole mass of water in the lake.

Indeed, it is very questionable whether any earthquake waves are ever produced in the ocean, except when the sea-bottom undergoes a permanent vertical displacement.
_Lake Tahoe_.