The sediments of the past are many miles in collective thickness: yet the feeble silt of the rivers built them all from base to summit.

He entered Trinity College Dublin in 1876 graduating in Engineering in 1882 in first place with various special certificates in branches of engineering at the same time obtaining a First Class Honours in modern literature. Joly served as President of Section C (Geology) when the British Association for the Advancement of Science which met in Dublin in 1908 during which he presented his paper "Uranium and Geology" an address to the society. It was the first successful process for producing color images from a single photographic plate.

He is also known for developing techniques to accurately estimate the age of a geological period based on radioactive elements present in minerals.