Darwin saw Quail Island as his key to understanding the structure of St. Jago, and made careful studies of its stratigraphy in the way he had learnt from Adam Sedgwick.
Darwin a considerat Insula Potârnichii drept cheia înțelegerii structurii insulei St. Jago, și i-a studiat cu grijă stratigrafia după metodele învățate de la Adam Sedgwick.