While I do not disagree with msucog, the D-2488 provides a method for an individual to classify soils based soley on visual characteristics and feel. If applied consistently by a single individual, you will get results that can be correlated from one boring to the next and identify layering distinctions in a boring. This is the true job of a field geologist, to be consistent. For that purpose and only that purpose, you can use it without testing or further corroboration - after all does it really matter whether you call a fat clay slippery gray mud or a sandy silt easy-to-crack clay, as long as you're consistent?
To convert the field information to universally accepted vernacular, I would agree the field geologist (or geotechnical engineer) should assign representative samples for classification via D-2487. Then it's just a simple matter of converting all of the slippery gray mud descriptions to fat clay and all the easy to crack clays to sandy silt.
f-d
¡papá gordo ain’t no madre flaca!