Complex sentence: A map dated 1776 (4) shows the cottage in some detail, and already extended (or, perhaps more likely, incorporating the 1725 dwelling) and describes it as being part of "Thomas Barrow's Farm".
Split into simpler sentences: A map dated 1776 (4) shows the cottage in some detail, and already extended (or perhaps more likely, incorporating the 1725 dwelling). It is described as being part of "Thomas Barrow's Farm".