1846.] Jlgricultural Geology of Onondaga County. 171 



The passage from the Marcellus shales to the Hamilton group 

 is easy, and effected by a gradual increase of angular sand, or 

 sand which has been less washed than usual. The color is less 

 dark, showing a diminution of carbonaceous matter. Lithologi- 

 cally, the Hamilton group is composed of dark colored slate and 

 shale, with numerous beds of thin sandstone, and still shaly, or 

 rather in that condition in which the silex or sand is rarely harsh 

 or gritt^". Some beds are brown from the presence of iron. The 

 matter which increases in the ascending order is sand; and hence, 

 in some of the superior beds we find sandstone well developed. 

 We are looking at those changes for the purpose of learning the 

 effect on the soil. Analysis and observation both show an in- 

 crease in the amount of silex, the diminution of calcareous and 

 aluminous matter, and the almost total disappearance of magnesia 

 in the rocks. We ahvays however get a trace of the latter, and 

 we may without doubt expect its presence in all rocks, but in 

 such small quantities that cultivated lands whose crops are re- 

 moved must in a few years be deficient in it. On ascending to 

 these superior rocks we find that the husbandry has changed; a 

 grazing district has taken the place of a wheat growing one. 

 This change, however, may not be due entirely to changes in the 

 composition of the formations. The country has become decidedly 

 hilly. We now find steep slopes, inclined surfaces, deep ravines, 

 rounded hills: in fine, all the characteristics of good fields and 

 walks for sheep and cows, for sweet grass and pure streams of 

 water. 



We deem it unnecessary to speak of the rocks which succeed 

 the Hamilton group. W^e may be permitted, however, to bring up 

 for once, considerations respecting the fossils of the rocks we have 

 adverted to and briefly described. Beginning with the red marl 

 and proceeding to the water lime series, we have a blank as it 

 regards life; but in the water lime series fossiles occur, but they 

 are very diflferent from those which had before existed. This 

 blank in the red and green shales mark an era in the history of 

 organic existence. Going above the water lime series, and we 

 are brought to another change; we leave behind all those beings 



