Source · the work in full

Notes, Critical and Explanatory, on the Holy Scriptures

PD · Francis Patrick Kenrick, Baltimore, 1849–1860 (Gospels 1849; Acts, Epistles & Apocalypse 1851; Psalms, Wisdom books & Canticle 1857; Job & the Prophets 1859; Pentateuch 1860)
Chapter 24

Exodus 24

Such was the appearance of the place on which the feet of the representative of the Deity rested. As no figure was presented to view, the lower part of the vision is understood by the feet.

You arrive at the cited line; the whole work is yours to read around it. The text is set from the cited public-domain edition.