Kirtley F. Mather, professor of Geology Emeritus, an expert on mineral resources and an outspoken critic of McCarthyism, died Sunday at the Presbyterian Hospital in Albuquerque, New Mexico. He was 90 years old.

Mather "was able to be a fine scientist as well as a humanist who lived by the ethical principles he stood for," Stephen J. Gould, professor of Geology, said yesterday.

As chairman of the Massachusetts Civil Liberties Union from 1946 to 1949, Mather became an early and forthright foe of former Sen. Joseph McCarthy's tactics for exposing alleged communists.

When an interviewer asked his opinion of the televised Army-McCarthy hearings in 1954, Mather said they were, "a magnificent thing" that allowed the public to have "direct observations of the methods used in investigations of this sort: guilt by association, built by accusation, use of innuendo, distortion of facts, use of half-truths when the whole truth presents a different picture."

Born in Chicago, Ill. on February 13, 1888, Mather received a B.S. degree in geology from Denison University in 1909 and a Ph.D. from the University of Chicago in 1915. He taught at the University of Arkansas, Queen's University in Canada and Denison University before coming to Harvard in 1924 as an associate professor. He became professor of Geology in 1927 and professor emeritus in 1954.

Mather's many books include "Old Mother Earth,""Science in Search of God," and"The Earth Beneath Us,"which won the 1964 publication award of the Geographical Society of Chicago as "the best book on science for lay readers."

A memorial service at Memorial Church will be scheduled.