It is a mountainous country intersected with rocky canons and fertile valleys, which occasionally broaden out into alluvial plains like that of the Shelif, or the Metija near Algiers, or those in the neighbourhood of Oran and Bona.
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.
Sometimes the tunnel was so narrow that the wheels of the buggy grazed the sides; then it would broaden out as wide as a street; but the floor was usually smooth, and for a long time they travelled on without any accident.
Next to my own dear teacher, he has done more than any one else to enrich and broaden my mind.