Format of Category/Archive Pages

What is the default setting for the Category and Archive pages, full post or excerpt? I am getting full post but I want excerpts.

The reason I am asking is that when I first set up my website I could not get excerpts on the home page. After some experimentation I found that the Mobile Theme in the Jetpack plugin was causing the problem. I deactivated it and was able to get excerpts.

Before I experiment some more, I would like to know if full posts on the Category and Archive pages is the default setting.

Thanks