The book is a fairly complete study of the descendents of John ROUND. The author studied census records, probates, wills, land records, marriage records, etc for literally hundreds if not thousands of ROUND(S) descendents. He includes some info on matrilineal families. When he found the info the names of spouses and that spousal info is included.
There are many missing ROUND(S) lines in the book. The author, while well-respected in genealogical circles, appears to either have missed individuals living in the same towns, appearing on the same census records, and having marriage, land and other records as many who were included in the book or left them out purposely. Before copying, you should have your line checked to see if it is included. The book covers primarily the first 6 generations but does have some info on a few later descendents.
There was another family of ROUND(S) which descends from a Mark ROUND(S). Mark Round(S) shows up in the US about the same time as John but seems to have gone north into Maine. His line is not researched for this book.