William Logan, the British administrator of Malabar, is known for authoring the:

Kerala Manual
Cochin Gazetteer
Malabar Manual
Travancore State Manual

The correct answer is: C) Malabar Manual.

William Logan was a British administrator who served in Malabar, India, from 1872 to 1882. He is best known for authoring the Malabar Manual, a comprehensive gazetteer of the Malabar region. The Malabar Manual was published in 1887 and is considered to be a valuable resource for information on the history, geography, and culture of Malabar.

The other options are incorrect. The Kerala Manual is a gazetteer of the state of Kerala, India. The Cochin Gazetteer is a gazetteer of the former princely state of Cochin. The Travancore State Manual is a gazetteer of the former princely state of Travancore.