hemispherical cells 28 in this manner the vermiculite particles form a cap 30 between the layers of cellular glass block 26 vermiculite is an irreversibly compressible material so that upon application the vermiculite particles compress under preloading to fill the open cells 28 of the cellular glass blocks a concrete bearing ring 32 is cast upon the glass block insulation ring 26 and serves as the base for the inner wall 14 of the double wall cryogenic tank 10 with the concrete bearing ring 32 in place a glass block insulation base 34 is set upon the leveling screed 24 within the glass block insulation ring 26 as with the glass block insulation ring 26 a vermiculite capping 30 is applied on the cut face of each of the cellular glass blocks of the insulation base 34 to penetrate and fill the open hemispherical cells thereof a sand pad 36 is spread over the capped surface of the upper course of cellular glass block base 34 to approximately the level of the upper surface of the concrete bearing ring 32 with this arrangement the upper surface of the concrete bearing ring 32 and the sand pad 36 receive the base plate 38 for the inner wall 14 thus the base plate 38 of the inner wall 14 is insulated by the array of cellular glass blocks 26 and 34 having the vermiculite capping 30 the construction of the cryogenic tank 10 is completed by providing a fiber glass expansion blanket 40 in abutting relationship with the inside surface of the outer.