No Topic Sentence

A paragraph without a clear topic sentence can be very hard to follow. The reader has to concentrate very hard to understand the point the writer is making.

For example, read the following paragraph:

When lightning strikes sand the heat sometimes fuses the sand into long, slender glass tubes called fulgurites, which are commonly called petrified lightning. The intense heat of a volcanic eruption also sometimes fuses rocks and sand into a glass called obsidian.

Compare the previous paragraph to this one.

In the second version of the passage, the addition of a topic sentence helps orient the reader to the issue under discussion.