The GN had eleven cars, 21950 to 21961 (one number not used), which were used for hauling "foundry sand". These were wood-sheathed cars, from the 45000-52999 series, and lasted into the BN era. Unlike some of the cars mentioned here, they kept their full-height side ladders.
Interestingly, one of these cars is believed to be the only GN boxcar ever painted Vermillion Red with BSB-style lettering. I haven't found an online picture, but one can be found in Four Ways West's "GN Equipment Pictorial Vol 1".