Finding texts about Australian Aboriginal religion in the public domain was extremely difficult. There is a landslide of 19th and early 20th Century books and articles about American and African indigenous traditions, many treating the subject with sensitivity and great depth. Only a few Australian works from this period are available, and most of them are pretty vague on the details. Some of this can be attributed to the traditional tribal secrecy, which is maintained even to this day.
Please be mindful of the historical context in which these books were written. The obvious problem with these books is that they were written by White Australians during the early twentieth century. This material contains racist and sexist characterizations, inaccurate depictions of aboriginal life and misrepresentations of their spiritual practices. Some of these documents contain completely fictional material which was the invention of the author, and have no actual basis in aboriginal belief or traditions. Descriptions of some of the ceremonies in these documents or the naming of dead people may regrettably violate Aboriginal tabus. These texts are provided for scholarly purposes and should not be considered definitive material on Aboriginal culture, only as a starting point for discussion.
In short, we encourage you to 'read between the lines'.
Native Tribes of the Northern Territory of
Australia by Baldwin Spencer. 
Images of Australian Rock Art
Native Tribes of
Works of K. Langloh Parker
Australian Legendary Tales collected by K.
Langloh Parker, Introduction by Andrew Lang. 
The Euahlayi Tribe by K. Langloh Parker.
Introduction by Andrew Lang. 
The following texts are of historical interest.
The Customs and Traditions of the Aboriginal
Natives of North Western Australia by John G. Withnell. 42,061 bytes.
The Aborigines of Western Australia by Albert F. Calvert.
Some Myths and Legends of the Australian Aborigines By William Jenkyn Thomas 
Australian Legends By C.W Peck