1883. ] Geology and Paleontology. 1055 
It is well known that on the most arid portions of the Colorado 
desert, when accidentally irrigated by the overflow of the river, a 
dense and luxuriant growth of vegetation springs up from seeds 
and germs which must have lain dormant for many years. 
Certain localities in California have become unhealthy on the 
introduction of water for mining purposes or irrigation, and in 
many cases the country, before healthy, has become almost unin- 
habitable from this cause. May not the same effect be produced 
by germs brought by the winds? I leave the answers to these 
questions to members of our society who have made a special 
study of disease germs, and will conclude with a calculation I 
have made of the quantity of dust that fell in San Francisco, 
based on the weight obtained and quantity of snow, as found in 
my experiments. Of course such a calculation can only be 
roughly approximate. Without going into details, my calcula- 
tion gives seventy-five tons to the square mile, supposing the fall 
to have been uniform. It is fair to assume that the upper air is 
frequently charged with dust, a portion of which falls near the 
source, while a larger portion is carried to unknown localities, and 
that the falling snow on the occasion of the December storm 
gathered it together and deposited it in our streets. 
__ Dr. Sternberg addressed the society upon the points presented 
in Mr. Hanks’ paper. He said he had spent much time in micro- 
he Evidences of Evolution. Among the evidences cited were 
those furnished by the Ungulate Mammalia whose development 
Since the beginning of Tertiary time (the Puerco epoch) is so 
distinctly marked in the skeleton and the brain, He gave a syn- 
Opsis of these in tabular form as follows: 
