He did say other things about Duluth. In his 1897 book Following the Equator, Mark Twain describes seeing a boat from Duluth while in Fiji and provides this description: 

In the afternoon we sighted Suva, the capital of the group [of islands], and threaded our way into the secluded little harbor—a placid basin of brilliant blue and green water tucked snugly in among the sheltering hills. A few ships rode at anchor in it—one of them a sailing vessel flying the American flag; and they said she came from Duluth! There’s a journey! Duluth is several thousand miles from the sea, and yet she is entitled to the proud name of Mistress of the Commercial Marine of the United States of America. There is only one free, independent, unsubsidized American ship sailing the foreign seas, and Duluth owns it. All by itself that ship is the American fleet. All by itself it causes the American name and power to be respected in the far regions of the globe. All by itself it certifies to the world that the most populous civilized nation, in the earth has a just pride in her stupendous stretch of sea-front, and is determined to assert and maintain her rightful place as one of the Great Maritime Powers of the Planet. All by itself it is making foreign eyes familiar with a Flag which they have not seen before for forty years, outside of the museum. For what Duluth has done, in building, equipping, and maintaining at her sole expense the American Foreign Commercial Fleet, and in thus rescuing the American name from shame and lifting it high for the homage of the nations, we owe her a debt of gratitude which our hearts shall confess with quickened beats whenever her name is named henceforth. Many national toasts will die in the lapse of time, but while the flag flies and the Republic survives, they who live under their shelter will still drink this one, standing and uncovered: Health and prosperity to Thee, O Duluth, American Queen of the Alien Seas!