don't get distracted by the misnomer sdcard. For historical reasons it often means your 8gig area and not a physical sdcard. Your 8gig area actually has sdcard in the directory name, and a real sdcard is something like blah/sdcard/sdcard!
I forgot how my claims can't be verified with the stock file browser. But on es file explorer, if you do a long press on any file on the root, and press properties... it shows your path is sdcard/. So everything you can access is a virtual sdcard to apps that access it that way. Go into any file on a physical sdcard, long press, and properties shows a path of sdcard/sdcard/!
Whew, this exercise motivated me to do more battle with google books reader and it's awful human factors. By exploring every obscure setting I made readibility half way tolerable, and sure got a huge world of books - especially 80+ year old freebies out of copyright. There is supposed to be a way google can provide epub formats to aldiko for easier reading, but that appears to be for paid ones only?
EDIT> At first I found it hard to search free books on google books app, until I found if you do a magnify lense search it will pop up a "free" button on upper right which you can click. Then you get out of the mode where it only shows you essentially the same free books as aldiko does, and can find a gazillion on any obscure subject. But I can't seem to narrow it down to languange type like the pc version of google book search.