"those that have been lately set forth in certain French novels"

The French were rather more daring than the English in their 18th century novels, exploring themes of eroticism, seduction, manipulation, and social intrigue.  Robert Browning, in his Soliloquy of the Spanish Cloister published in 1842, warned of the dangers in such reading materials:

Or, my scrofulous French novel

On gray paper with blunt type!

Simply glance at it, you grovel

Hand and foot in Belial’s gripe (Belial is the personification of evil in the Old Testament, and a fallen angel in Milton’s Paradise Lost).

Marquis de Sade, the most notorious of the Libertines
Public DomainMarquis de Sade, the most notorious of the Libertines - Credit: H. Biberstein

But the French (and indeed the Italians) didn't stop at scandalous plotlines.  Erotic prints had been popular in Europe from the middle of the fifteenth century.  These often portrayed the ancient Greek gods in explicitly sexual acts (because the subject matter was from the Classical period, it was justified as a legitimate and above-board art form).  By the 17th century, numerous examples of pornographic or erotic literature has begun to achieve a wider circulation.  These included L'Ecole des Filles, a French work printed in 1655 that is considered to be the beginning of pornography in France.  Samuel Pepys, writing in his diary, confessed to purchasing a copy for solitary reading, and then burning it so that it would not be discovered by his wife. 

During the Enlightenment, many of the French Libertines began to exploit pornography as a medium of social criticism and satire, often targeting the Catholic Church and general attitudes of sexual repression. Mass-produced, inexpensive pamphlets brought pornography to the masses.  By the early 18th century, the English upper classes were terribly worried about the morals of women and the working classes being corrupted by the ready availability of these salacious materials.