The Indian plate and Eurasia collided between 40 and 60 million years ago according to four observations, one being that there is no mammalian fossil record in India from around 50 million years ago. On its way, the Indian plate passed over the Reunion hotspot which led to volcanic activity, thus forming the Deccan Traps. Its collision with the Eurasian plate led to the rise of the Himalayas and the continuous tectonic activity still makes it an earthquake prone area. The Gangetic plains were formed by the deposition of silt by the Ganga and its tributaries into the area between the Himalayas and the Vindhya range. The rock formations can be divided into the Archaean, Proterozoic (Dharwar system), Cuddupah system, Vindhyan system, Gondwana system, The Deccan Traps, Tertiary system, Pleistocene period and recent formations.