"The Waning of the Middle Ages" is a historical analysis of the cultural life of the late Middle Ages, particularly in France and the Low Countries, during the 14th and 15th centuries. It delves into the period's modes of thought, forms of expression, religious beliefs, and social norms. The book argues that the era was characterized by a highly stylized and overwrought civilization, marked by an excessive emphasis on chivalry and courtly love, a religious mindset dominated by the fear of death and the afterlife, and a cultural milieu that was both highly imaginative and deeply pessimistic.

"Decline of the West" is a comprehensive historical and philosophical work that explores the rise and fall of civilizations. The author argues that every civilization has a life cycle, from birth to maturity and finally to decline. He suggests Western civilization is in its final stage of decline, comparing it to the end phases of the Greco-Roman civilization. The book also introduces the concept of 'pseudomorphosis', where a civilization is so deeply influenced by a previous culture that it suppresses its own authentic culture.

"The Origin of Continents and Oceans" presents the groundbreaking theory of continental drift, proposing that the Earth's continents were once joined together in a single landmass and have since drifted apart to their current positions. The author, a meteorologist and geophysicist, supports his hypothesis with extensive geological and paleontological evidence, showing similarities in rock formations, fossil records, and climatic patterns across different continents. Despite initial skepticism from the scientific community, this work laid the foundation for the modern understanding of plate tectonics and fundamentally changed the way we think about the Earth's surface and its dynamic nature.