sentences:  Despite many structural complications, the Nubian Sandstone likely constitutes a single hydrogeological system west of the Suez Gulf.To the east, on the Sinai Peninsula, a second system might exist with some connection to the primary western system in the north.The main western system, extending into Libya and Sudan, consists of a multi-layered artesian basin where massive groundwater reserves accumulated, principally during pluvials of the Quaternary.