Since a songline can span the lands of several different language groups, different parts of the song are said to be in those different languages. Languages are not a barrier because the melodic contour of the song describes the nature of the land over which the song passes. The rhythm is what is crucial to understanding the song. Listening to the song of the land is the same as walking on this songline and observing the land. Songlines have been described as a "cultural passport" which, when sung in the language of a particular region and mob, show respect to the people of that country. Neighbouring groups are connected because the song cycles criss-cross all over the continent. All Aboriginal groups traditionally share beliefs in the ancestors and related laws; people from different groups interacted with each other based on their obligations along the songlines. In some cases, a songline has a particular direction, and walking the wrong way along a songline may be a sacrilegious act (e.g. climbing up Uluru where the correct direction is down). Aboriginal people regard all land as sacred, and the songs must be continually sung to keep the land "alive". Their "connection to country" describes a strong and complex relationship with the land of their ancestors, or "mob". Aboriginal identity often links to their language groups and traditional country of their ancestors. Songlines not only map routes across the continent and pass on culture, but also express connectedness to country. Songlines are often passed down in families, passing on important knowledge and cultural values. Molyneaux and Vitebsky note that the Dreaming Spirits "also deposited the spirits of unborn children and determined the forms of human society", thereby establishing tribal law and totemic paradigms. Anthropologist Robert Tonkinson described Mardu songlines in his 1978 monograph The Mardudjara Aborigines - Living The Dream In Australia's Desert. In his 1987 book The Songlines, British novelist and travel writer Bruce Chatwin describes the songlines as: Examples The Yolngu people of Arnhem Land in the Northern Territory tell the story of Barnumbirr, a creator-being associated with the planet Venus, who came from the island of Baralku in the East, guiding the first humans to Australia, and then flew across the land from East to West, naming and creating the animals, plants, and natural features of the land. The Yarralin people of the Victoria River Valley venerate the spirit Walujapi as