As early as 1698 the slave-trade to South Carolina had reached such proportions that it was thought that “the great number of negroes which of late have been imported into this Collony may endanger the safety thereof.”  The immigration of white servants was therefore encouraged by a special law.[10] Increase of immigration reduced this disproportion, but Negroes continued to be imported in such numbers as to afford considerable revenue from a moderate duty on them.  About the time when the Assiento was signed, the slave-trade so increased that, scarcely a year after the consummation of that momentous agreement, two heavy duty acts were passed, because “the number of Negroes do extremely increase in this Province, and through the afflicting providence of God, the white persons do not proportionately multiply, by reason whereof, the safety of the said Province is greatly endangered."[11] The trade, however, by reason of the encouragement abroad and of increased business activity in exporting naval stores at home, suffered scarcely any check, although repeated acts, reciting the danger incident to a “great importation of Negroes,” were passed, laying high duties.[12] Finally, in 1717, an additional duty of L40,[13] although due in depreciated currency, succeeded so nearly in stopping the trade that, two years later, all existing duties were repealed and one of L10 substituted.[14] This continued during the time of resistance to the proprietary government, but by 1734 the importation had again reached large proportions.  “We must therefore beg leave,” the colonists write in that year, “to inform your Majesty, that, amidst our other perilous circumstances, we are subject to many intestine dangers from the great number of negroes that are now among us, who amount at least to twenty-two thousand persons, and are three to one of all your Majesty’s white subjects in this province.  Insurrections against us have been often attempted."[15] In 1740 an insurrection under a slave, Cato, at Stono, caused such widespread alarm that a prohibitory duty of L100 was immediately laid.[16] Importation was again checked; but in 1751 the colony sought to devise a plan whereby the slightly restricted immigration of Negroes should provide a fund to encourage the importation of white servants, “to prevent the mischiefs that may be attended by the great importation of negroes into this Province."[17] Many white servants were thus encouraged to settle in the colony; but so much larger was the influx of black slaves that the colony, in 1760, totally prohibited the slave-trade.  This act was promptly disallowed by the Privy Council and the governor reprimanded;[18] but the colony declared that “an importation of negroes, equal in number to what have been imported of late years, may prove of the most dangerous consequence in many respects to this Province, and the best way to obviate such danger will be by imposing such an additional duty upon them as may totally prevent the evils."[19] A prohibitive duty of L100 was accordingly imposed in 1764.[20] This duty probably continued until the Revolution.