It is marked by grey clays and sands, lignitic fossiliferous clays, beds of lignite or brown coal, sometimes 8 ft.
The Jackson formation south-west of the Lisbon beds, is made up chiefly of grey calcareous clay marls, bluish lignitic clays, green-sand and grey siliceous sands.
The coal underlying the east half of the state, the " Great Plains," is lignitic and of inferior quality, but that in the mountain districts is bituminous and generally suitable for coking.
Coal and lignitic coal are the principal economic minerals met with in this central plain, though natural gas occurs and is put to use near Medicine Hat, and " tar sands " along the northeastern edge of the Cretaceous indicate the presence of petroleum.
The true bituminous coal produced, which in 1897 was only equal to that of the lignitic and semi-bituminous varieties (1.75 million tons), had come by 1902 to constitute three-fourths (5.46 million tons) of the entire coal output.
