1898] JAMES HALL 263 
That office and the similar position for the state of Wisconsin, 
which Hall received in 1857, he was able to hold without affecting 
his position in the New York service. His work in connection with 
these surveys increased his knowledge of the geology of the Missis- 
sippi basin; and he was able to make important additions to the 
geology of the western states, as he was entrusted by the Federal 
Government with the description of the collections made by 
many of the expeditions and surveys in that region. Thus he 
described the fossils collected by the Fremont expedition, the 
collections of the Pacific Railway Survey, the Cretaceous fossils 
obtained by the Mexican Boundary Commission, and wrote a 
report on the geology and palaeontology of the basin of the Great 
Salt Lake of Utah from materials brought back by Lieutenant 
. Stansbury. 
In 1856 Hall was elected President of the American Association 
for the Advancement of Science. At its meeting in Montreal in the 
following year he gave his famous address, in which was first 
definitely expounded the theory that the elevation of mountain chains 
is due to the deposition of sedimentary deposits, and that the direction 
of the mountain chains are determined by lines along which the 
thickest accumulation has taken place. 
But this and similar incursions into the domain of physical 
geology only temporarily distracted Hall from palaeontographical 
work to which his inexhaustible energies were mainly devoted. 
His additions to the materials of invertebrate palaeontology are 
probably greater than those of any other man. The number of 
important new genera founded by Hall is enormous. The roll of 
Hall’s new genera and species was by 1858 so long, that Colonel 
Portlock, the President of the Geological Society whose duty it was 
to present Hall with the Wollaston Medal, felt bound to qualify his 
patronizing commendations by a warning that he was himself “ prone 
to hesitate respecting new species when closely allied to previously 
known species.” But the work which Colonel Portlock appeared to 
disparage is now recognised as Hall’s most permanent title to fame. 
As a note in the Geological Magazine reminds us, palaeontology is 
indebted to Hall for the following important genera: among the 
eraptolites there are Callograptus, Dicranograptus and Phyllograptus ; 
among the corals, Coelophyllum, Heliophyllum and_ Streptelasma ; 
among the Pelmatozoa, Calceocrinus, Heterocrinus, Dendrocrinus, 
Glyptaster, Glyptocrinus and Hemicystis; there is the star-fish 
Palaeaster, and the echinid Lepidechinus; the additions to the 
Monticuliporoids and Bryozoa are very numerous, including Favistella, 
Callopora, Bactropora, and Trematopora; and among the Trilobites 
are Plewronotus, Bathynotus, Mesothyra and Ptychaspis. His Memoir 
on North American Hurypterida, Pterygoti and Ceratiocaris (1871), 
