In chapter 2 of The Just Men of Cordova by Edgar Wallace, the author was describing a business man in London:
His was a name to conjure with in certain circles. In others it was never mentioned. The financial lords of the City—the Farings, the Wertheiners, the Scott-Teasons—had no official knowledge of his existence. They went about their business calmly, loaning their millions at a ridiculously small percentage, issuing Government loans, discounting bills, buying bullion, and such-like operations which filled the hours between eleven o’clock, when their electric broughams set them down in Threadneedle Street, and four o’clock, when their electric broughams picked them up again. They read of Colonel Black in their grave way, because there were days when he dominated the financial columns. They read of his mighty stock deals, of his Argentine electric deal, his rubber notations and his Canadian copper mines.
Does "in their grave way" mean "with their serious attitude"?
And what's exactly meant by "rubber notations", is it "rubber figures"?