578 METASPERMAE OF THE MINNESOTA VALLEY. 
The climate is a characteristic inland North American one. 
The rainfall has its source almost entirely in the Gulf of Mexico 
vapors which extend up the Mississippi valley, precipitating 
themselves in less and less amount as they pass from the 
mouth of the Minnesota river to its headwaters. A summer 
maximum of precipitation is conspicuous. The temperature 
is, of course, less thau that of points on the same parallels in 
the old world, such as Marseilles, Florence or Odessa. It pre- 
sents conspicuous summer maxima and winter minima.—40° 
Fahr. is reached occasionally during the months of January or 
February, and—30° Fahr. frequently. In the summer, 95° Fahr. 
is reached occasionally and 90° Fahr. during almost every 
summer. The variations are more excessive in the western 
and prairie regions than in the eastern and forest regions, 
where the range of maxima and minima is least. The shelter- 
ing effects of the forest, the lower altitude, and possibly the 
smaller width of the valley, by interfering with cold or hot 
winds, have much to do with this difference. The snow-fall is 
greatest in the northwestern portion. The first frosts usually 
occur near the middle of September, and the ice breaks up in 
the streams late in March or early in April. 
Phaenological observations. No reliable phaenological ob- 
servations have been made in the valley of the Minnesota. In 
general, as elsewhere in the northern hemisphere, the plants 
of the northern range are first to flower, and those of most 
southern range last. The time of flowering of any species is a 
useful indication of its history, and observations along this line 
are muchneeded. The first shrub to put forth leaves is usually 
Artemisia dracunculoides, the first trees to flower, the various 
species of Salix. In the autumn a characteristic composite- 
flowering is seen in the golden-rods, asters and sunflowers of 
both prairie and forest region. The mid-summer season finds 
the prairies gay with the purple of Laciniaria and Astragalus or 
Spiesia. The oaks are usually among the last trees to drop 
their leaves, and the cottonwoods among the first. Among 
herbaceous plants chlorophyll persists the longest in the 
grasses. 
Geological history of the Minnesota valley. The Minne- 
sota river of today occupies an ancient gorge which was evi- 
dently formed previous tothe Cretaceous period, for Creta- 
ceous clays are found in eroded hollows of the Shakopee lime- 
stone in Le Sueur, Nicollet and Blue Earth counties and Cre- 
taceous sandstones, clays and shales in the Cottonwood and 
