guide, as it has ceased to apply to the use of airspace above a height which may interfere with the ordinary user of land [cf Bernstein, above]". The Supreme Court nevertheless upheld the claimant's right to claim for trespass at depths of 250 to 400 metres below the surface, whilst acknowledging that subterranean ownership could not extend indefinitely; albeit compensation for such a trespass would be very small as there was no interference in any practical sense with the land through which the pipe was passed. The decision has subsequently been restricted by section 43 of the Infrastructure Act 2015, which permits the exploitation of 'deep level land' (defined as land more than 300 metres below the surface) for certain purposes without liability for trespass. This was passed as a statutory alienation of rights over freehold registered land that proprietors have to facilitate 'fracking', and would have permitted some (though not all) of the intrusions in the Bocardo case. United States In the United States, the end of the indefinitely upward interpretation of the ad coelum doctrine came from a well-reasoned United States Supreme Court case United States v. Causby in 1946. In the Causby case: low-flying military planes caused the plaintiffs' chickens to "jump up against the side of the chicken house and the walls and burst themselves open and die". The plaintiffs sued the government, arguing that they were entitled to compensation under the takings clause of the Fifth Amendment. The court's decision, authored by Justice William O. Douglas, could have resolved the case on a narrow ground by simply holding that there was a taking of land because the government's flights affected the land. Justice Douglas did reach that conclusion, but then he went much further and opined on what airspace landowners do and do not own. He wrote that "if the landowner is to have full enjoyment of the land, he must have exclusive control of the immediate reaches of the enveloping atmosphere. Otherwise buildings could not be erected, trees could not be planted, and even fences could not be run". Thus, a landowner "owns at least as much of the space above the ground as he can occupy or use in connection with the land", and invasions of that airspace "are in the same category as invasions of the surface". The Causby case rejected the notion that property ownership extended upward 'indefinitely', while still recognizing