When the gradually falling temperature reaches 1430° (q), the mass begins to freeze as -y-iron or austenite, called " primary " to distinguish it from that which forms part of the eutectic. But the freezing, instead of completing itself at a fixed temperature as that of pure water does, continues until the temperature sinks to r on the line Aa.
At the second retardation, K" (Ar2, about 770°) this ferrite changes to the normal magnetic a-ferrite, so that the mass as a whole becomes magnetic. Moreover, the envelopes of ferrite which began forming at Ar 3 continue to broaden by the accession of more and more ferrite born from the austenite progressively as the temperature sinks, till, by the time when Ar t (about 690°) is reached, so much free ferrite has been formed that the remaining mother-metal has been enriched to the composition of hardenite, i.e.
On the other hand the chain between the Great St Bernard and the Simplon sinks at barely half a dozen points below a level of 10,000 ft.
Thence to the Reschen Scheideck Pass the main chain is ill-defined, though on it rises the Corno di Campo (10,844 ft.), beyond which it runs slightly north-east past the sources of the Adda and the Fra g ile Pass, sinks to form the depression of the Ofen Pass, soon bends north and rises once more in the Piz Sesvenna (10,568 ft.).
(b) On the other hand, if from the Dreiherrenspitze we cleave to the true main watershed of the Alpine chain, we find that it dips south, passes over the Hochgall (11,287 ft.), the culminating point of the Rieserferner group, and then sinks to the Toblach Pass, but at a point a little east of the great Dolomite peak of the Drei Zinnen it bends east again, and rises in the Monte Coglians (9128 ft., the monarch of the Carnic Alps).