220 Geology of the Country between 
possible manner. It is no easy task to reduce this confusion to sys- 
tematic arrangement, and there seems abundant room for diversity of ' 
opinion, with but little danger of any one proving bis opponents in the 
-wrong or himself in the right. It is indeed difficult to convey a cor- 
rect idea of the primitive strata along this part of our section. Slaty 
and crystalline granite appear to predominate, mixed with slates and 
a rock approaching hornblende rock in external character. The 
granite may be well seen in the neighborhood of Ellicott’s mills, 
where there are extensive quarries that furnish vast quantities for the 
Baltimore market. Succeeding the primitive rocks, next appear 
transition slates and sandstones, exhibiting the usual Protean varie- 
ties of the transition graywacke formation. I use this last term in 
the general sense adopted by Humboldt, who designates by it* “ ev- 
ery conglomerate, sandstone and fragmentary or arenaceous rock of 
transition formation that is anterior to the red sandstone and coal for- 
mation,” with this addition, that I would also include within the same 
definition all those transition slates that we find interstratified with the 
above conglomerates and sandstones, and which must have been of 
nearly contemporaneous origin. This would include the argillite in 
all its varieties, the old red sandstone, the millstone grit and the gray- 
wacke, and graywacke slate of Prof. Eaton, as members of the same 
formation. There would at first sight seem but little analogy be- 
tween the soft roof slate of commerce, and the harsh quartzose con- 
glomerate that is quarried for millstones. But the wide difference 
between these disappears when we find, first, this conglomerate chang- 
ing its character and passing gradually into finer sandstone, next, the 
sandstone becoming more slaty and alternating with beds of genuine 
argillite. Prof. Eaton has observed that Europeans do not under- 
stand their graywackes, and I might safely add that no one can well 
understand the graywackes of this country without visiting the moun- 
tains of Pennsylvania and Virginia. ‘This formation, which is colored 
brown on the section, commences on the west of the primitive rocks, 
that are colored red, and continues uninterruptedly to the Monocacy, 
including the elevated ground known as Parr’s ridge. ‘Throughout 
this whole distance, its peculiar variable characters are strikingly ex- 
hibited. The slaty varieties often appear somewhat talcose, often 
shining as if varnished, at one time friable and rapidly disintegrating, 
and again firm and compact. At one place quarries have been open- 
* Supenposition of Rocks, p. 201. 
