Complex sentence: Only the southern portion of the once vast township continued to adhere to the township form of government and it was composed of swamps, marshes, farmlands, and, except for a few clustered enclaves, isolated homesteads.
Split into simpler sentences: Only the southern portion of the once vast township continued to adhere to the township form of government. That remaining portion was composed of swamps, marshes, farmlands, and, except for a few clustered enclaves, isolated homesteads.