Full Idea
What (in the analysis of substances) exist ultimately are simple substances - namely, souls, or, if you prefer a more general terms, 'monads', which are without parts.
Gist of Idea
All substances analyse down to simple substances, which are souls, or 'monads'
Source
Gottfried Leibniz (Metaphysical conseqs of principle of reason [1712], §7)
Book Reference
Leibniz,Gottfried: 'Philosophical Writings', ed/tr. Parkinson,G.H.R. [Dent 1973], p.175
A Reaction
This seems to me to be atomistic panpsychism. He is opposed to physical atomism, because infinite divisibility seems obvious, but unity is claimed to be equally obvious in the world of the mental. Does this mean bricks are made of souls? Odd.