~Changes in Rivers.~--Allusion has already been made to the changes which the courses of Panjab rivers are subject to in the plains. The Indus below Kalabagh once ran through the heart of what is now the Thal desert. We know that in 1245 A.D. Multan was in the Sind Sagar Doab between the Indus and the united streams of the Jhelam, Chenab, and Ravi. The Bias had then no connection with the Sutlej, but ran in a bed of its own easily to be traced to-day in the Montgomery and Multan districts, and joined the Indus between Multan and Uch. The Sutlej was still flowing in the Hakra bed. Indeed its junction with the Bias near Harike, which probably led to a complete change in the course of the Bias, seems only to have taken place within the last 150 years[2]. FOOTNOTES: [Footnote 2: Raverty's "The Mehran of Sind and its Tributaries," in _Journal of Asiatic Society of Bengal_, 1897.] CHAPTER IV GEOLOGY AND MINERAL RESOURCES ~Extent of Geological Record.~--Although the main part of the Panjab plain is covered by a mantle of comparatively recent alluvium, the provinces described in this book display a more complete record of Indian geological history than any other similar area in the country. The variety is so great that no systematic or sufficient description could be attempted in a short chapter, and it is not possible, therefore, to do more in these few pages than give brief sketches of the patches of unusual interest. ~Aravalli System.~--In the southern and south-eastern districts of the Panjab there are exposures of highly folded and metamorphosed rocks which belong to the most ancient formations in India. These occupy the northern end of the Aravalli hills, which form but a relic of what must have been at one time a great mountain range, stretching roughly south-south-west through Rajputana into the Bombay Presidency. The northern ribs of the Aravalli series disappear beneath alluvial cover in the Delhi district, but the rocks still underlie the plains to the west and north-west, their presence being revealed by the small promontories that peep through the alluvium near the Chenab river, standing up as small hills near Chiniot in the Shahpur, Jhang, and Lyallpur districts.