LAMINATED PYROCRYSTALLINE ROCKS. 
97 
all that part of the United States which lies east of and upon 
the Appalachians, is supplied most abundantly with this valua¬ 
ble ore of iron. It skirts this great range for more than a 
thousand miles; ai^d though not by any means continuous, still it 
occurs at convenient intervals, and at such points as can not 
fail to supply the wants of over six millions of inhabitants. 
OF THE LAMINATED PYROCRYSTALLINE ROCKS. 
§ 68. Lamination and cleavage planes. Much has been said 
with a view to elucidate the efficient cause which has operated 
in the production of planes of lamination, or planes of cleav¬ 
age. A phenomenon which is universal, is not to be attributed 
to local influences. Local influences are adjurants, but not the- 
efficients of change. The wide-spread derivative matter, on 
the ocean’s bottom, consisting of fine sand, clays and lime, 
mingled together, are a mere mechanical mixture, mingled 
together without order. But it is found that slates which are 
the results of such mixtures, have undergone, in process of time, 
very great changes. But the rocks referred to slates, differ 
much in the amount of change which they have suffered. 
Some are hard and ringing, others soft and fragile. Those which 
belong to the first, do not usually occupy their original position, 
but they are inclined, and appear to have been acted upon by 
mechanical forces, to a much greater extent than the latter. 
Pressure, therefore, must be recognized as a force which has 
had something to do in converting them into hard and firm 
slates, and in developing the peculiar structures of slaty masses. 
But pressure is an adjurant to an efficient cause, and this effi¬ 
cient cause must be referred to some of the essential properties 
of matter or to original endowments. This original endowment 
is probably crystallization. I have had occasion to speak of 
this property before. I have also employed the term, molecu¬ 
lar force, a term which I have used where the result is the 
formation of spheroids, or rather nodular masses, while crystal¬ 
lization produces parallelograms upon a large scale. In the 
formation of the planes of parallelograms, pressure aids the 
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