The Mentor Beds. — ('r<i(jiii. 163 
which, strewn with huge rectangular bh)cks of quartzytic 
sandstone, is known as Battle hill. Thej^ are supposed to ap- 
pear to some extent also in Kice, Marif)n, and Dickinson coun- 
ties, though their presence there still lacks confirmation, and 
in Marion and Dickinson they must be limited to the northern 
and southern parts of the counties respectively. 
The shales of the Mentor beds are chiefly argillaceous, but they 
contain a greater or less admixture of sand, to which, as soft 
sandstones, they locally give place in certain horizons. They 
apparently contain some lime also, partly in the condition of 
sulphate. Being little consolidated, they weather into gentle 
slopes and broad, low, rounded eminences scarcely worthy the 
name of hills, and present few conspicuous outcrops. Such 
outcrops of the shales as do occur present themselves either as 
limited, more or less steep-faced banks of marly-appearing 
clay, of white, ferruginous-yellow, red, or blue color, or parti- 
colored with two or more of these. Their coloring seems to be 
the result of the variable distribution of oxide, peroxide, and 
sulphates of iron. 
The sandstone of the Mentor beds occurs in thin, local 
strata. While these are of slight consequence judged by the 
space they occupy, they are nevertheless of great stratigraphic 
importance, since it is from these alone that our knowledge of 
the geological age of the Mentor terrane has been derived. 
So soft is this sandstone that its natural outcrops rarely present 
themselves as integral ledges, but commonly as slopes scattered 
with lumps and slabs of sandstone, representing the hardest and 
most dura1)le i)arts of a vanished bed; but occasionally ap- 
pears a ledge that is considered sutticiently hard and uniform 
to ])e quarried, yielding a rather soft and poor (luality of 
building-stone. Some quarries of this sort, belonging to the 
Mentor beds, may be seen in the district between Bavaria and 
Soldier (!ap mound. 
The thickness of th<^ Mentor beds varies greatly, since that 
portion of the terrane that rests directly upon the Permian 
lies unconformalily upon the latter and presents consideral)le 
differences in the elevation of its base. It probably nowiiere 
greatly exceeds fifty or sixty feet. 
The fauna of the Mentor beds, so far as at present known, 
is included in the following list: 
