@ucbalumnus, OK, less than a quarter is probably an exaggeration, but for instance, a history major at UIUC requires 36 credit-hours: http://www.history.illinois.edu/undergraduate/major/
An astronomy major at UIUC requires less than a quarter of classes in astronomy (26 credit-hours) but does have math and physics requirements as well: http://www.astro.illinois.edu/academics/undergraduate/major/