Sentence:  It now turns out that the Pitch Lake, like most other things, owes its appearance on the surface to no convulsion or <WSD>vagary</WSD> at all, but to a most slow, orderly, and respectable process of nature, by which buried vegetable matter, which would have become peat, and finally brown coal, in a temperate climate, becomes, under the hot tropic soil, asphalt and oil. 
Meaning of the word marked with <WSD> tags:  An erratic, unpredictable occurrence or action.