A memory array comprising strings of memory cells comprises laterally-spaced memory blocks individually comprising a vertical stack comprising alternating insulative tiers and conductive tiers. Channel-material-string structures of memory cells extend through the insulative tiers and the conductive tiers. The channel-material-string structures individually comprise an upper portion above and joined with a lower portion. Individual of the channel-material-string structures comprise at least one external jog surface in a vertical cross-section where the upper and lower portions join. Other embodiments, including method are disclosed,