On your demo here – http://www.kriesi.at/themes/abundance/blog/ the blog page has ‘Read more’ and displays an excerpt. However on my blog page, which I’ve tried to create via the dynamic templates and an archive template, the whole post appears.
Inside the content of the posts, try to add this code:
This is how to use it:
This way, the content will be cut and a read more link will appear (plus you can control where the content will be cut). Also try to go to: Settings > Reading and set For each article in a feed, show to Summary. Hope this helps.