Excellent question! I'm always happy to see that someone is trying to cite sources properly. First - citing an e-book is not only appropriate, but it is very useful to other researchers, because they can look at your source. As for formatting, you may want to look at WikiTree's Sources Style Guide for reference. My personal tip (because I am always looking for a shortcut!) is to go to http://www.worldcat.org/, type in the title, and select the title from the list. In the upper right corner you will see a "Cite/Export" link. Cicking on that link allows you to select from several citation styles - the Chicago Style is the preferred style on WikiTree (according to the Sources Style Guide). Then you can copy and paste it into your profile. Here's your reference:
Crowell, Edwin, and Arnold Doane. 1923. A history of Barrington township and vicinity, Shelburne County, Nova Scotia, 1604-1870: with a biographical and genealogical appendix. Yarmouth, Nova Scotia: Crowell.
Because it is an e-book, you will also want to link to it. You can do this by placing the URL in square brackets with the reference. I can explain it better with an example:
[url citation]
So your reference would be listed as:
[https://archive.org/stream/historyofbarring00crowuoft/historyofbarring00crowuoft_djvu.txt Crowell, Edwin, and Arnold Doane. 1923. A history of Barrington township and vicinity, Shelburne County, Nova Scotia, 1604-1870: with a biographical and genealogical appendix. Yarmouth, Nova Scotia: Crowell.]
In your profile, it will display only your citation, and you can click on it to get to the e-book.
Sorry this answer is so long. It actually takes less time to do than it does to explain!