| 21. | The lower boundary is taken at the transition from red continental shales of the Lunde formation to the overlying sandstones.
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| 22. | The lower boundary of the Cambrian was originally held to represent the first appearance of complex life, represented by trilobites.
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| 23. | The lower boundary of the Floian is defined as the first appearance of " Tetragraptus approximatus ", a graptolite species.
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| 24. | The Ergilian's lower boundary is the approximate base of the Priabonian age and approximate upper base of the Rupelian age.
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| 25. | The arms lie on an unseen parapet coinciding with the lower boundary of the painting, according to the Flemish painting tradition.
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| 26. | It is very likely that further investigations will push back the Sri Lankan lower boundary to match that of South India.
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| 27. | The lower boundary coincides with the ground ( or, more precisely, a height above ground corresponding to its aerodynamic roughness ).
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| 28. | Earth may in fact lie on the lower boundary of habitability : if it were any smaller, plate tectonics would be impossible.
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| 29. | Landslips often occur at or close to the lower boundary of the Tunbridge Wells Sands, between it and the underlying Wadhurst Clay Formation.
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| 30. | The Tabenbulakian's lower boundary is the approximate base of the Chattian age and upper boundary is the approximate base of the Aquitanian age.
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