Also mentioned is that Seurat did a good deal of preparation before making his large, Pointillist paintings -- understandable, given their subject matter, composition and coloring. Part of this preparation involved smaller studies. And before that phase of his career he did paint many small works that had an impressionist feeling.
This is the painting Seurat is most famous for.
Here is the earliest Seurat that I could locate. Done while attending the École des Beaux-Arts.
An early post-Army painting. Wispy and not nearly as solidly conceived as most of this later works, but at this point, he was probably just experimenting with Impressionist ideas.
A mix of a few well-defined and ill-defined forms. Brushwork is nondescript.
Brush strokes here are more obvious.
Stronger brushwork for the riverbank, similar to what is found in the following images.
A good deal of hatching brushwork in the vegetation.
I found this at the Norton Simon in Pasadena. It's a small study (compare its size to the information plaque). The museum's web site deals with it here.