In the winter months of 1969, shortly after the completion of Miners and Merchants in Bourbon Mexico, I returned to the archives of Mexico. In that book I had argued that ‘the Mexican hacienda was a sink through which drained without stop the surplus capital accumulated in the export economy’. But for the historian, as much as for the scientist, hypothesis often runs ahead of available evidence. It was now time to verify this proposition. Anxious to avoid a wild goose chase for random data, a procedure bound to turn up material biased in favour of my case, I chose to concentrate on haciendas in the Bajío, the region most affected by eighteenth-century expansion of silver production. In the event, only Léon was found to possess a continuous series of records. The scholar may propound his questions, but it is the sources which prescribe the limits of the answers. In point of fact, the very reliance on public documents, be they municipal, notarial or parochial, precluded any sustained treatment of the central issue of the original hypothesis – the rate of agricultural profit and its relation to capital investment. Only the internal accounts of individual haciendas will yield a satisfactory resolution of this problem. Similarly, without access to such papers it was difficult to obtain any sure impression of the organisation of production or the disposition of the work-force within the great estate.