 Complete the following phrase:  He made extensive and important researches in the coal, oil, and iron fields of the United States and Canada and became State geologist of Pennsylvania in 1874. From 1872 to 1878 he served as professor of geology at the University of Pennsylvania; after 1886 he was emeritus professor. The year 1863 he spent in Europe, examining the Bessemer ironworks in Sheffield for the Pennsylvania Railroad Company, and in 1867 he was one of ten commissioners sent by the United States Senate to the 