scratch the surface

scratch the surface AND scrape the surface (discover or deal with a very small part of a subject) — пройтись по верхам; очень поверхностно рассмотреть что-л.; поверхностно коснуться какой-л. темы; поверхностно затронуть какую-л.; ≅ затронуть тему в общих чертах, в первом приближении; ≅ галопом по европам

Example 1: There's far more to be said — I've only had time to scratch the surface in this talk.

Example 2: We left feeling that we had just scratched the surface of this fascinating country.

Example 3: Up to now newspaper articles have only scratched the surface of this tremendously complex issue.

see also
[quick trot through sth]
skate over sth

Example: We'll skate over this next chapter (allwords.com)