When Alfred Wegener first made his case for continental drift, he relied on two main lines of argument: the shape of the continents and the relative positions of glacial till deposits. Evidence later accumulated from other areas of research, but the theory was not taken seriously until well after Wegener's death.
The first argument Wegener put forward in support of his theory was that the continents seemed to fit together like the pieces of a jigsaw puzzle. This relationship is apparent from a map, but the exactness of the match improves if the underwater continental shelves are compared. The true edges of South America and Africa, for example, fit together to a high degree of precision, allowing for millions of years of erosion.
Wegener's second argument was more complex. He traveled the world and charted the locations and orientation of glacial till deposits. These deposits are the alluvial remnant of a glacier's progress across the landscape, and they remain long after the glacier has melted away. By plotting out the latitudes of ancient till deposits, Wegener was able to demonstrate that, for his evidence to be consistent with unmoving continents, much of the world would have had to be covered in ice sheets in the relatively recent past, even in the tropics. He argued that this was evidence that the tropical continents had once been at higher latitudes.