en GEOLOGY OF OHIO. 
enumerated in the preceding chapters, the Quaternary has already been 
briefly discussed ; but while the other groups are so simple that a few 
words may suffice to convey a clear idea of them, or at least of the new 
things we have learned about them, the Drift phenomena are too com- 
plicated, too little understood, and too interesting to be so summarily 
dismissed. It is true, also, that the causes that produced such marked 
effects in Ohio during the Quaternary age, covered in their action a 
much wider field than any one state or county; and for a proper under- 
standing of the facts observed here, it is necessary that the record made 
elsewhere should be consulted. Although the last formed of all the geo- 
logical series, and for this reason presenting the fullest and freshest 
record, the deposits of the Quaternary age have been the most difficult 
of all to decipher. The significance of facts observed in one locality be- 
comes apparent only by comparing them with those seen in other and 
distant places; and it is by this process alone that any intelligent idea 
has been gained of the remarkable sequence of events which took place 
in the Quaternary age. I have, therefore, thought it best to include in 
this sketch of the Drift of Ohio brief notices of the observations made 
on similar phenomena outside of our State limits, and such as constitute 
the basis of the theories which have been proposed for the solution of 
the problems of the Quaternary. We shall thus be able to estimate 
more justly the import of our observations, and shall see how far they 
confirm or controvert the views that have been heretofore advanced. 
The most important facts which the study of the Drift has brought to 
light are, briefly, as follows: 
Ist. Over the northern half of North Amercia, and down as low as the 
fortieth parallel of latitude, we find, not every where, but in most localities 
where the nature of the underlying rocks is such as to retain inscrip- 
‘tions made upon them, the upper surface of these rocks ground or planed 
off, or furrowed and striated in a peculiar and striking manner, evidently 
-by the action of one great denuding agent. It is now agreed by all 
geologists that this agent was ice. There has been some difference of 
opinion as to whether this ice rested upon land, or floated upon water ; 
in other words, whether it formed glaciers or icebergs; but no one who 
‘has seen glaciers, and has observed the effect they preduce on the rocks 
‘over which they move, and who examines good exposures of the mark- 
ings to which I have reference, will fail to pronounce them the products 
-of glacial action. The track of a glacier is as unmistakable as that of a 
man or a bear, and is as significant and trustworthy as any other legible 
inscription. | 
Though having a general north and south direction, locally the glacial 
