Maria, The ships took finished goods and people to North America and, for quite a long time, the product coming back was timber. Even when the Colonies reached the point of producing excess for export, timber remained the greatest need in Great Britain. The return loads were of more weight and bulk than those of the westward crossing. That's where all the cobblestones originated in the East Coast port cities. They were ballast in the arriving ships that wasn't needed for the return. -- Jo-Ann Croft