Allied to this phase, yet differing from it, is the “Zona Libre” or Free Zone, 12 miles broad and 1,833 miles long, which forms the northern hem of Mexico from the Gulf to the Pacific.  Here foreign goods pay only 18-1/2 per cent., formerly only 2-1/2 per cent., of the usual federal duties.  Goods going on into the interior pay the rest of the tariff at the inner margin of the Zone.  This arrangement was adopted in 1858 to establish some sort of commercial equilibrium between the Mexican towns of the Rio Grande Valley, which were burdened by excessive taxation on internal trade, and the Texas towns across the river, which at this time enjoyed a specially low tariff.  Consequently prices of food and manufactured goods were twice or four times as high on the Mexican as on the American side.  The result was persistent smuggling, extensive emigration from the southern to the northern bank, and the commercial decline of the frontier states of Mexico, till the Zona Libre adjusted the commercial discrepancy.[364] Since 1816 a tariff free zone a league wide has formed the border of French Savoy along the Canton and Lake of Geneva, thus uniting this canton by a free passway with the Swiss territory at the upper end of the lake.[365]

[Sidenote:  Boundary zones of mingled race elements.]

When the political boundary has evolved by a system of contraction out of the wide waste zone to the nicely determined line, that line, nevertheless, is always encased, as it were, in a zone of contact wherein are mingled the elements of either side.  The zone includes the peripheries of the two contiguous racial or national bodies, and in it each is modified and assimilated to the other.  On its edges it is strongly marked by the characteristics of the adjacent sides, but its medial band shows a mingling of the two in ever-varying proportions; it changes from day to day and shifts backward and forward, according as one side or the other exercises in it more potent economic, religious, racial, or political influences.

Its peripheral character comes out strongly in the mingling of contiguous ethnic elements found in every frontier district.  Here is that zone of transitional form which we have seen prevails so widely in nature.  The northern borderland of the United States is in no small degree Canadian, and the southern is strongly Mexican.  In the Rio Grande counties of Texas, Mexicans constituted in 1890 from 27 to 55 per cent. of the total population, and they were distributed in considerable numbers also in the second tier of counties.  A broad band of French and English Canadians overlaps the northern hem of United States territory from Maine to North Dakota.[366] In the New York and New England counties bordering on the old French province of Quebec, they constitute from 11 to 22 per cent. of the total population, except in two or three western counties of Maine which have evidently been mere passways for a tide of habitants moving on to more attractive conditions of life in the counties just to the south.[367] But even these large figures do not adequately represent the British-American element within our boundaries, because they leave out of account the native-born of Canadian parents who have been crossing our borders for over a generation.