"Lost History"

I began reading this book today (by Michael Hamilton Morgan) and am a bit perplexed. It is published by the National Geographic Society, so I expect some bias in it, however, there seems to be a serious lack of citations. While he does include a rather short bibliography at the end, he does not cite any of his sources within the text itself. I am only about halfway through the first chapter (each chapter is roughly 40 pages long). I want to use this book as a source, but I am finding that I may not be able to due to the citation issue. How can a "scholar" write a book on any subject and NOT cite their sources? While what I have read so far sounds fairly accurate from an historical standpoint (I base this on the previous research I have done in my field of study during my undergraduate education and some classes I have taken), how can I justify using it as a source for my thesis??