The phrase "deepest portion" refers to the part of something that is farthest down or at its lowest point.
Sentences with «deepest portion»
The temperature change is indicative of water circulating through the crust and uppermost mantle beneath mid-ocean spreading centers, and the heat from deeper portions of the mantle being dissipated through contact with the cooler upper rocks. (astrobio.net)
Over the subsequent 4.5 billion years of Earth's evolution, convection in Earth's interior, like water boiling on a stove, caused deep portions of the mantle to rise upwards, melt, and then separate once again by density. (carnegiescience.edu)
Ezra is just ready to move on to the deeper portion of the playard, but the bassinet came in handy for gently putting him down without waking him. (happeningsoftheharperhousehold.net)