A paragraph may move from cause to effects or from an effect to its causes. The topic sentence in the following paragraph mentions an effect; the rest of the paragraph lists several causes.

The fantastic water clarity of the Mount Gambier sinkholes results from several factors. The holes are fed from aquifers holding rainwater that fell decades—even centuries—ago, and that has been filtered through miles of limestone. The high level of calcium that limestone adds causes the silty detritus from dead plants and animals to cling together and settle quickly to the bottom. Abundant bottom vegetation in the shallow sinkholes also helps bind the silt. And the rapid turnover of water prohibits stagnation.

—Hillary Hauser, “Exploring a Sunken Realm in Australia”