12 



The Vegetation of the 



The great coal-field, occupying two-thirds of the State of Illinois, is 

 covered by the northern drift, which is spread over the Northern Missis- 

 sippi Valley southward to 39° north latitude. That this drift once filled 

 the whole river valley, and that this was afterward washed out, is sufii- 

 ciently proved by the large holders found along the river banks, granit, 

 syenit, diorit, porphyr, etc., that were brought by icebergs from the far 

 north and dropped during melting; they were left when the softer 

 material was floated away. 



The bottom soil is alluvial; on the upland we find, below the humus, 

 a subsoil of alternating layers of loam and gravel. There is no limestone 

 soil, or very rare. There is little chance in the flora of Peoria to make 

 observations on relations between chemical qualities of the soil and vegeta- 

 tion, if we would not attribute significance to the growth of certain grasses 

 on pure sand soil. It is always the physical condition the habitat of each 

 species depends upon: exposition to sunshine or shade, loose or compact 

 ground, dryness of humidity of the soil and similar contrasts are favorable 

 or exclusive. 



CLIMATE. 



As generally in the middle parts of the great continents of the northern 

 hemisphere our climate is an excessive one. Hot summers, cold winters 

 and a rapid change of temperature at all seasons is the character of this 

 climate. 



Table 1. 



TEMPERATURE, Dec. 1, 1855 to Nov. 30, 1885. 



The range of the thermometer scale in thirty years comprised 132° 

 and nearly the same (127) even in one year 1872, when in January the 

 minimum was — 22 and the maximum in August 105. The lowest stand 

 of the mercury — 27 was observed on the 5th of January, 1884. The 

 greatest range in one month (January, 1874,) was 87° from — 22 to 65, 



