If the several formations in these regions have not been deposited during the same exact periods-a formation in one region often corresponding with a blank interval in the other-and if in both regions the species have gone on slowly changing during the accumulation of the several formations and during the long intervals of time between them; in this case the several formations in the two regions could be arranged in the same order, in accordance with the general succession of the forms of life, and the order would falsely appear to be strictly parallel; nevertheless the species would not all be the same in the apparently corresponding stages in the two regions.
Baldin herrialdeotan formazio ezberdinak aldi berberetan metatu ez badira,-sarri herrialde bateko formazioa besteko hutsarteari egokituz-eta herrialde biotan espezieak, formazio ezberdinen metaketa aldian eta haien arteko denbora tarte luzeetan, astiro-astiro aldatuz joan badira, kasu honetan herrialde bietako formazio ezberdinak ordena berean eraturik gera zitezkeen, forma organikoen hurrenketa orokorraren arabera, eta ordenak hertsiki paraleloa emanen luke, nahiz eta egia ez izan; hala ere, espezieak ez ziren guztiak berdinak izanen itxuraz elkarri zegozkien herrialde bietako etapetan.