首楞嚴義疏注經 6.253

6.253

持地菩薩因平心地，見內、外塵本無自性，不相觸摩，皆如來藏。今揀地性堅礙有為，體非通達，不成聖性，故非圓通。

The Bodhisattva Dharaṇīṃdhara, through leveling the ground of the mind, saw that internal and external dusts fundamentally lack self-nature and do not touch or rub each other, being entirely the tathāgatagarbha. Here it is selected out: the nature of earth is solidly obstructive and conditioned; its substance is not penetrative and does not constitute the noble nature; therefore it is not perfect penetration.