The Lalbagh hill is composed of dark biolite gneiss of granitic to granodioritic composition containing streaks of biolite. Vestiges of older rocks are seen in the form of enclaves within the gneiss.
Peninsular Gneiss of the region is dated 2500 to 3400 million years that accreted in three major episodes, i.e. 3.4 Ga, 3.3–3.2 Ga and 3.0–2.9 Ga. The quarries of Lalbagh are of great importance for researches on earth sciences towards evolution of the terrain.

Geological Survey of India: National Geological Monument: This monument is over a typical exposure of peninsular gneiss, a geological term for complex mixture of granitic rocks extensively developed in peninsular India. The term was coined by Dr. W.F. Smeeth of Mysore Geological Department in 1916. The peninsular gneiss is among the oldest rocks of the earth dating back to 10 years old. The antiquity of these rocks has attracted geologists all over the world and has given rise to erudite scientific papers on the evolution of the earth by the pioneers of the Mysore Geological Department, Geological Survey of India and scholars from the academy. Stone quarry of this gneiss still continues to be an endless source material for research in the various branches of earth science.