Sentence:  At a centre-point of a conurbation containing all but a fraction of mankind, and this at twice or three times mankind's present numbers, the pressure of human activity on the unimaginable <WSD>Ecumenopolitan</WSD> centre-point would be as enormous as the water-pressure of the Ocean on the Ocean's bottom at the points at which the Ocean is at its deepest. 
Meaning of the word marked with <WSD> tags:  Of or characteristic of the Ecumenopolis.