Complex sentence: Nothing visible remains on the site, as local landowners took away much of the stone for their own buildings, and by 1840, the North Woolwich railway was built through the site, and factories were established on the remaining land.
Split into simpler sentences: Nothing visible remains on the site, as local landowners took away much of the stone for their own buildings. By 1840, the North Woolwich railway was built through the site, and factories were established on the remaining land.