Darwin worked up his "Sketch" into a 189-page '"Essay"' and in July entrusted the manuscript to the local schoolmaster to copy. He then wrote a difficult letter to be opened by his wife in the event of his death requesting that the essay be published posthumously. He started his "Geological Observations on South America", and corresponded with Hooker about this, feeding in questions related to his "Essay". The copied "Essay", now 231 pages, was returned to him for corrections in September. Then one day he brought it to Emma and asked her to read it. She went through the pages, making notes in the margins pointing out unclear passages and showing where she disagreed.