The Fort Worth Basin which lies beneath Cretaceous sediments west of Dallas formed as a foreland basin during the Ouachita orogeny. Horizontal shortening caused flexural isostasy to bend the lithosphere. The bent lithosphere to the west of the Ouachita mountains caused a bowl-shaped depression to form, known as a foreland basin, preserving the Mississippian sediments of the Barnett Shale and other Paleozoic sediments; these sediments mostly formed before the Pangeic collision. Significant deposits of hydrocarbons such as natural gas have economic importance as is seen in formations like the Barnett Shale.