Question: What type of genre did Robery Ranke's Graves White Goddess fit into?

Context paragraphs:
The White Goddess: The White Goddess: a Historical Grammar of Poetic Myth is a book-length essay on the nature of poetic myth-making by author and poet Robert Graves.  First published in 1948, the book is based on earlier articles published in "Wales" magazine, corrected, revised and enlarged editions appeared in 1948, 1952 and 1961.  "The White Goddess" represents an approach to the study of mythology from a decidedly creative and idiosyncratic perspective.  Graves proposes the existence of a European deity, the "White Goddess of Birth, Love and Death," much similar to the "Mother Goddess", inspired and represented by the phases of the moon, who lies behind the faces of the diverse goddesses of various European and pagan mythologies.

Holly King (archetype): The Holly King is a speculative archetype of modern studies of folklore and mythology which has been popularized in some Neopagan religions.  In his book "The White Goddess", the author Robert Graves proposed that the mythological figure of the Holly King represents one half of the year, while the other is personified by his counterpart and adversary the Oak King: the two battle endlessly as the seasons turn.  At Midsummer the Oak King is at the height of his strength, while the Holly King is at his weakest.  The Holly King begins to regain his power, and at the Autumn Equinox, the tables finally turn in the Holly King's favor; his strength peaks at Midwinter.  Graves identified a number of paired hero-figures which he believes are variants of this myth, including Lleu Llaw Gyffes and Gronw Pebr, Gwyn and Gwythr, Lugh and Balor, Balan and Balin, Gawain and the Green Knight, the robin and the wren, and even Jesus and John the Baptist.

Robert Graves: Robert von Ranke Graves (24 July 1895 – 7 December 1985), also known as Robert Ranke Graves and most commonly Robert Graves, was an English poet, novelist, critic and classicist.  In a way similar to Oscar Wilde, Robert Graves was a Celticist and student of Irish mythology, by the influence of his father Alfred Perceval Graves, a celebrated Irish poet — with William Wilde, these families were inheritors of the Gaelic revival.  He produced more than 140 works.  Graves's poems—together with his translations and innovative analysis and interpretations of the Greek myths; his memoir of his early life, including his role in the First World War, "Good-Bye to All That"; and his speculative study of poetic inspiration, "The White Goddess"—have never been out of print.  Irish literature deeply affected Graves' White Goddess theories, specifically the genre aisling.

Druantia: Druantia is a hypothetical Gallic tree goddess proposed by Robert Graves in his study "The White Goddess" (1948).

Homer's Daughter: Homer's Daughter is a 1955 novel by Robert Graves, famous for "I, Claudius" and "The White Goddess".

Leucothea: In Greek mythology, Leucothea (Greek: Leukothea (Λευκοθέα), "white goddess") was one of the aspects under which an ancient sea goddess was recognized, in this case as a transformed nymph.

Ino (Greek mythology): In Greek mythology Ino ( Greek: Ἰνώ ] ) was a mortal queen of Thebes, who after her death and transfiguration was worshiped as a goddess under her epithet Leucothea, the "white goddess."  Alcman called her "Queen of the Sea" (θαλασσομέδουσα), which, if not hyperbole, would make her a doublet of Amphitrite.

Charles Patrick Graves: Charles Ranke Patrick Graves (1 December 1899 – 21 February 1971) was a journalist and writer, and brother of Robert Graves.

Seven Days in New Crete: Seven Days in New Crete, also known as Watch the North Wind Rise, is a seminal future-utopian speculative fiction novel by Robert Graves, first published in 1949.  It shares many themes and ideas with Graves' "The White Goddess", published a year earlier.

Saint Albina: The name Albina comes from Albina, "the White Goddess," the Etruscan goddess of the dawn and protector of ill-fated lovers.  It was a common name in ancient Rome.  According to Nennius, Britain gains its earliest name, Albion from Albina, the White Goddess, the eldest of the fifty Danaids, possibly originating from the German words "elf-woman".

Supporting paragraphs: The White Goddess Robert Graves
Answer: Poetic Myth