Geoscience Reference
In-Depth Information
rocks. The volumewas reissued in 1944 in a revised formby Shimer and
Robert Rakes Shrock (b. 1904). While it is still of some use, perhaps
of greatest value to geologists today is the multi-volume work Treatise
on Invertebrate Paleontology which has been published since 1953 by
the Geological Society of America and the University of Kansas Press.
Conceived by the stratigrapher and palaeontologist Raymond C.
Moore (1892-1974) it provides separate volumes for different biological
groups. Each genus is described and illustrated and their age range is
given. It is the foremost identification aid available.
CORRELATION CHARTS
Todaymany geologists who study particular periods in geological time
do not confine themselves to limited geographical regions, but
attempt to learn what was happening geologically in other more
widely flung districts worldwide. To do this they have to rely on
correlation charts. One of the earliest such documents was that
arranged by the English geologist Bernard Hobson (1860-1933), a lec-
turer in petrology at Owens College, Manchester, whose charts pro-
vided data for Britain and Ireland. In the late 1960s the Geological
Society of London took it upon itself to establish a number of commit-
tees each given the task of producing detailed correlation charts and an
accompanying explanatory volume of British and Irish strata in one of
the geological Periods. By the late 1970s most Periods were covered
and in fact in the past ten years a number of reports have been revised
in the light of new findings. Similarly correlation charts for North
America have been published by the United States Geological Survey
and by the Geological Survey of Canada, and many other areas have
these aids to correlation. On a local scale correlation charts are easier
to produce than those on a global scale. For some geological Periods
global standards exist, for others they are piecemeal and global stan-
dards are in the process of being formulated and agreed. Such agree-
ments may take decades.
Another problem facing compilers of correlation charts is that of
terminology. Many names have been used for geological horizons that
