"I differ materially from Capt. Lewis, in my account of the numbers, manners, and morals of the Sioux"

Zebulon Pike was an American explorer who took a trip to the Midwest in the early 1800s. In this quote, he is referring to his distinctions with Captain Meriwether Lewis, who had likewise explored the area. Pike is stating that he has a different viewpoint than Lewis on the numbers, good manners, and morals of the Sioux, a Native American tribe in the region. This could mean that Pike believes there are more Sioux than Lewis thought, or that their habits and worths are various than what Lewis observed. It could also indicate that Pike has a various opinion on the Sioux's general character. Whatever the distinctions may be, Pike is making it clear that he has a various opinion than Lewis on the Sioux. This might be due to the reality that Pike invested more time with the Sioux, or that he had a different perspective on them. Whatever the case, it is clear that Pike and Lewis had different views on the Sioux.