In 1837 he visited the United States .
In 1837 he acquired there the materials for papers on the thermal springs and the geology of North America , read in 1838 before the Ashmolean Society and the British Association ( and published in 1839 ) .
In 1837 he visited the United States and acquired there the materials for papers on the thermal springs and the geology of North America , read in 1838 before the Ashmolean Society and the British Association ( and published in 1839 ) .