Ladies, Ladies, Ladies. Look closely.
The quilt is made from one block. "Mary's Square" is just the name the author of that particular book gave it. It probably has a bazillion other names, too. It's very common for public domain blocks to have more than one name.
By changing the colors, rearranging the placement of lights, mediums and darks, and rotating the blocks in a variety of ways, you can achieve any number of different looks. Nancy Jean has shown us two and will soon re-post her drawings that illustrate more.
In the meantime, here's a basic file showing the shapes that make up the block. It can be done with rotary cutting, with templates, or as a paper-piecing project.
The file includes one page of blank blocks. Print a few copies. Cut them apart and play with the blocks. Rotate, rearrange, color them in with pencils or crayons. You will find yourself playing with them for hours as you discover all the possibilities. :P