"Quick Scroll may appear on the bottom-right corner of the page, showing one or more bits of text from the page that are relevant to your query. Clicking on the text will take you to that part of the page. Quick Scroll appears only when it is likely to be useful."
The extension uses the snippet generated for a search result and tries to locate each excerpt, but this approach isn't always successful because some snippets are obtained from meta tags or from the Open Directory Project.
Google Quick Scroll is one of the many Chrome extensions created by Google. To install them, you need Google Chrome 4 Beta (Windows, Linux).