In previous articles, the authors have outlined the general principles underlying the study of the subject of paper defects, and have reported an investigation of photomicrographic, electrical, and microchemical methods for detection of metallic particles in paper. It is the purpose of this article to extend the study to the origin and identification of more of the important types of spots and specks encountered generally in pulps and papers, and to present an atlas of such objectionable foreign particles. By this means, it is hoped the student of paper defects and many mill technologists will be enabled to reduce to a systematic and simple science a branch of paper technology which hitherto has required a combination of great skill, knowledge, and extensive individual experience. -- CAL