Śatapatha Brāhmaṇa ("of a hundred paths") 7.4.2.30

7.4.2.30

tadyadete atropadadhāti | saṃvatsara eṣo 'gnirima u lokāḥ saṃvatsarastasyāyameva lokaḥ prathamā citirayamasya loko vasanta ṛtustadyadete atropadadhāti yadevāsyaite ātmanastadasminnetatpratidadhāti tasmādete atropadadhāti

And as to why he now lays down these two;--this Agni (fire-altar) is the year, and the year is these worlds; the first layer is this (terrestrial) world thereof, and the spring season also is this world thereof; and when he now lays down those two (bricks), he thereby puts back into him (Agni-Pragâpati) what those two (the first layer and the spring) are to that body of his: this is why he now lays down those two (bricks).