Integrated circuitry comprising a memory array comprises strings of memory cells comprising laterally-spaced memory blocks that individually comprise a first vertical stack comprising alternating insulative tiers and conductive tiers. Strings of memory cells comprise channel-material strings that extend through the insulative tiers and the conductive tiers. The conductive tiers individually comprise a horizontally-elongated conductive line. A second vertical stack is aside the first vertical stack. The second vertical stack comprises an upper portion and a lower portion. The upper portion comprises alternating first insulating tiers and second insulating tiers. The lower portion comprises a lowest insulator tier directly above conductor material of a conductor tier. The lowest insulator tier comprises solid carbon and nitrogen-containing material. An immediately-adjacent tier is directly above the solid carbon and nitrogen-containing material of the lowest insulator tier. The immediately-adjacent tier comprises material that is of different composition from that of the lowest insulator tier. Other embodiments, including methods, are disclosed.