Explanation:

Indian subcontinent can be divided into three major geographical regions viz. The northern mountain systems, the Indo-Ganga-Brahmaputra plains and the Peninsular block.
The Peninsular block is the oldest geological feature among these and is mainly made up of ancient gneiss.
The northern boundary of the Peninsular Block may be taken as an irregular line running from Kachchh along the western flank of the Aravali Range near Delhi and then roughly parallel to the Yamuna and the Ganga as far as the Rajmahal Hills and the Ganga delta.
Apart from these, the Karbi Anglong and the Meghalaya Plateau in the northeast and Rajasthan in the west are also extensions of this block. The northeastern parts are separated by the Malda fault in West Bengal from the Chotanagpur plateau. It is believed that due to the force exerted by the northeastward movement of the Indian plate at the time of the Himalayan origin, a huge fault was created between the Rajmahal hills and the Meghalaya plateau. Later, this depression got filled up by the deposition activity of the numerous rivers. Today, the Meghalaya and Karbi Anglong plateau stand detached from the main Peninsular Block. 
In Rajasthan, the desert and other desert–like features overlay this block.
The Peninsula mostly consists of relict and residual mountains like the Aravali hills, the Nallamala hills, the Javadi hills, the Veliconda hills, the Palkonda range and the Mahendragiri hills, etc.  These mountains are very old and were once high and mighty. But now they have been eroded off to form small rounded hills
The river valleys here are shallow with low gradients. This is so because of Hard strata lying beneath the river beds and the general gentle gradient of the peninsular block.