Related Clues:
- Really long times
- Immense time periods
- Practical eternity
- Long times, in London
- Immeasurable spans
- Periods of two or more of 40-Across
- Immensely long stretches
- Billion-year time divisions
- Gorges are carved over them
- Many, many, many, many, many moons
- Practically an eternity
- Considerable stretches
- Interminable periods
- Canyons form over them
- Extensive periods