Rocks of the earliest part of the Cambrian Period are found in the Salt range in Punjab and the Spiti area in the central Himalayas and consist of a thick sequence of fossiliferous sediments. In the Salt range, the stratigraphy starts with the Salt Pseudomorph zone, which has a thickness of and consists of dolomites and sandstones. It is overlain by magnesian sandstones with a thickness of , similar to the underlying dolomites. These sandstones have very few fossils. Overlying the sandstones is the Neobolus Shale, which is composed of dark shales with a thickness of . Finally there is a zone consisting of red or purple sandstones having a thickness of to called the Purple Sandstone. These are unfossiliferous and show sun-cracks and worm burrows which are typical of subaerial weathering. The deposits in Spiti are known as the Haimanta system and they consist of slates, micaceous quartzite and dolomitic limestones. The Ordovician rocks comprise flaggy shales, limestones, red quartzites, quartzites, sandstones and conglomerates. Siliceous limestones belonging to the Silurian overlie the Ordovician rocks. These limestones are in turn overlain by white quartzite and this is known as Muth quartzite. Silurian rocks which contain typical Silurian fauna are also found in the Vihi district of Kashmir.