So much of either metal as is present in excess over the eutectic ratio, freezes out before the eutectic; (2) that though thus constant, its composition is not in simple atomic proportions; (3) that its freezing-point is constant; and (4) that, when first formed, it habitually consists of interstratified plates of the metals which compose it.
At Sao Joao da Chapada, in Minas Geraes, diamonds occur in a clay interstratified with the itacolumite, and are accompanied by sharp crystals of rutile and haematite in the neighbourhood of decomposed quartz veins which intersect the itacolumite.
If, however, we discover plantbearing strata interstratified with deposits containing marine fossils, we can fix the period to which the plants belong, and may be able to correlate them in distinct areas, even though the floras be unlike.
The individual beds, seldom more than a few feet in thickness and sometimes only a few inches, are interstratified with an immense thickness of quartzites.
It is the last part of the metal to undergo this transformation and, when thus transformed, it is of constant though not atomic composition, and habitually consists of interstratified plates of its component metals.
Serpentines, peridotites and diabases are interstratified with the Eocene deposits.
In short, from Ar 3 to Ar t the excess substance ferrite or cementite, in hypoand hyper-eutectoid steels respectively, progressively crystallizes out as a network or skeleton within the austenite mothermetal, which thus progressively approaches the composition of hardenite, reaching it at Ar t, and there splitting up into ferrite and cementite interstratified as pearlite.
When the mass is cooled, the carbon changes over into the condition of cementite as usual, partly interstratified with ferrite in the form of pearlite, partly in the form of envelopes enclosing kernels of this pearlite (see Alloys, Pl.
Immediately heals over any cracks which form in the small quantity of cementite interstratified with it in the pearlite of hypo-eutectoid steels.
Slates, schists, quartzites and limestones form the greater part of the hills, but the Brocken and Victorshohe are masses of intrusive granite, and diabases and diabase tuffs are interstratified with the sedimentary deposits.