water, they built "flash dams" or "driving dams" on smaller streams, so they could release water to push the logs down when they wanted. Each timber firm had its own mark which was placed on the logs, called an "end mark". Obliterating or altering a timber mark was a crime. At the mill the logs were captured by a log boom, and the logs were sorted for ownership before being sawn. Log drives were often in conflict with navigation, as logs would sometimes fill the entire river and make boat travel dangerous or impossible. Floating logs down a river worked well for the most desirable pine timber, because it floated well. But hardwoods were more dense, and weren't buoyant enough to be easily driven, and some pines weren't near drivable streams. Log driving became increasingly unnecessary with the development of railroads and the use of trucks on logging roads. However, the practice survived in some remote locations where such infrastructure did not exist. Most log driving in the US and Canada ended with changes in environmental legislation in the 1970s. Some places, like the Catalan Pyrenees, still retain the practice as a popular holiday celebration once a year. In Sweden legal exemptions for log driving were eliminated in 1983. "The last float in southern Sweden was in the 1960s, with the floating era in the rest of the country ending completely with the last of the many log drives in the Klarälven river in 1991." Popular culture The contemporary logrolling contest, Birling, is a demonstration of skills originally devised by log drivers. Inclusive description of a complex assortment as "the whole Mary Anne" derives from the colorful characters of wangan caravans which periodically transformed quiet rural communities with the excitement of a passing log drive. In Canada, "The Log Driver's Waltz" is a popular folk song which boasts about a log driver's dancing skills. The version of the Canadian one-dollar bank note issued in 1974 and withdrawn in 1989 featured a view of the Ottawa River with log driving taking place in the foreground and Parliament Hill rising in the background. This banknote was part of the fourth series of banknotes released by the Bank of Canada entitled "Scenes of Canada". The logs depicted in this bank note may have been destined for a half dozen pulp, paper and sawmills near the Chaudière Falls immediately upstream from Parliament Hill, or