At all events, they do enable us to distinguish between ports exclusively devoted to river traffic and those with direct relations to oversea ports. Nearly all the boats destined for the Parana touch at Buenos Aires, which remains the chief importing centre, on the way up, and unload there. They then go empty to Rosario, San Nicolas, or Santa Fe to take on a full cargo of cereals or timber, and set out down the Parana for Europe without calling at Buenos Aires. Clearances for interior navigation at the port of Buenos Aires are far more numerous than entries. From 1912 to 1914 Buenos Aires received on the average, coming from interior ports, 1,750,000 tons, of which 1,635,000 were cargo. It cleared for the same ports ships totalling 3,275,000 tons, of which 1,580,000 were in ballast. The latter figure fairly represents the tonnage of sea-going ships sent up river empty after discharging on the quays of Buenos Aires. At Rosario, San Nicolas and San Pedro, on the other hand, the tonnage of clearances for Argentine ports is much less than the tonnage of entries.[135] The total movement of goods at the port of Rosario is 410,000 tons entries and 375,000 tons clearances for interior navigation, and 1,100,000 tons entries and 1,824,000 tons clearances for navigation abroad. [135] Movement of internal navigation at Rosario (average 1912-1914): entries, 1,108,000 tons, of which 690,000 in ballast; clearances, 580,000 tons. At San Nicolas: entries, 400,000 tons, of which 440,000 in ballast; clearances, 4,000 tons. The difference between the entries and the clearances represents ships starting straight for Europe. According to Repossini's calculations the tonnage of exports on the lower Parana south of Santa Fe rose in 1910 to 4,000,000 or 4,500,000. The imports, almost entirely confined to Rosario, were about a fourth of this figure. For the middle and upper Parana, Repossini estimated the volume of the traffic at 800,000 tons, of which _quebracho_ was two-fifths.