Among the thousands of books published every year in this country, some are completely unnecessary. The Black Migration, a scattershot 20th century overview of the U.S. race problem, belongs in this category. Unnecessary not because the book is offensive or feebly researched (it isn't), nor because the subject matter is unimportant, nor because its organization is muddled and content diffuse (which is true), but because its author offers not a scintilla of original comment, perspective, or information on the black question. Leaning on the Myrdals, Moynihans, Clarks, Fraziers, and Census Bureau statistics (there are many tables), Groh describes the Jim Crow South, why Negroes began leaving in droves beginning after World War I, and their ongoing fate in the urban North. He tells you it's a myth that blacks were attached to their plantation masters; that ghetto life has a ""shattering effect on families""; that Black Power is ""probably an inevitable and necessary stage in the black emergence""; that ""white America does not fully recognize the blacks as human""; that ""We golf on the moon, but we cannot convert junk-strewn lots into places where children can run and play."" A case history of Newark is patched together from newspaper and magazine articles; a chapter on solutions to the black urban dilemma trots out old War on Poverty snake oil sprinkled with trendy local cooperative programs. Groh (whose last book -- also bad -- was Gold Fever, 1966) ends by saying blacks can't improve their position by relying on white ""liberal benevolence."" It's like telling us the Pope is Catholic.