Clay
This word is used of sediment found in pits or in streets (Isa 57:20; Jer. 38:60), of dust mixed with spittle (John 9:6), and of potter’s clay (Isa 41:25; Nah 3:14; Jer 18:1–6; Rom 9:21). Clay was used for sealing (Job 38:14; Jer 32:14). Our Lord’s tomb may have been thus sealed (Matt 27:66). The practice of sealing doors with clay is still common in the East. Clay was also in primitive times used for mortar (Gen 11:3). The “clay ground” in which the large vessels of the temple were cast (1 Kgs 7:46; 2 Chr 4:17) was a compact loam fitted for the purpose. The expression literally rendered is, “in the thickness of the ground,”, meaning, “in stiff ground” or in clay.
From Easton’s Bible Dictionary (1897), by Matthew George Easton.