Final answer:
The legal description is missing a necessary reference to a Principal Meridian or Baseline, which is essential in the Public Land Survey System to identify land parcels accurately and unequivocally.
Step-by-step explanation:
The legal description 'the NW1/4 of the SW1/4 of Section 6, Township 4 North, Range 7 West' is defective because it lacks reference to a Principal Meridian or a Baseline. Legal descriptions of land in the United States generally adhere to the Public Land Survey System (PLSS), which relies on a grid system to identify land parcels in many parts of the country. This system uses a combination of meridians (north-south lines) and baselines (east-west lines) to create a set of principal coordinates from which all other descriptions derive their locations.
The legal description provided names the aliquot parts (NW1/4 of the SW1/4) and the section, township, and range, which suggests a location within a specific township grid. However, without the reference to a specific Principal Meridian or Baseline, it is impossible to identify the exact piece of land with certainty as there could be multiple 'Section 6, Township 4 North, Range 7 West' across different meridians and baselines. Therefore, for a legal description to be recognized as complete and accurate, it must reference these crucial elements to avoid any ambiguity regarding the property's location.