His studies of ice-polished rocks in his Alpine homeland, far outside the range of present-day glaciers, led Louis Agassiz in 1837 to propose the concept of an age in which great ice sheets had existed in now currently temperate areas.

• Ain which great ice sheets had existed in now currently temperate areas  
• Bin which great ice sheets existed in what are now temperate areas  
• Cwhen great ice sheets existed where there were areas now temperate  
• Dwhen great ice sheets had existed in current temperate areas  
• Ewhen great ice sheets existed in areas now that are temperate