Geoscience Reference
In-Depth Information
Hooke also propounded theories on strata, noting that water was
the main agent of deposition but also of denudation, and he under-
stood that air or wind could also carry sediment: loess, a type of wind-
blown soil found in central Asia, is formed by such a mechanism. He
also said that volcanoes produced their own sediment in the shape of
ash that fell following an eruption and became compressed into rock
through the pressure from overlying sediments, which is true; and that
other methods of lithification were effected by sunlight which dried
out surface sediments. While baked muds do form in this way, it is rare
that they become consolidated and lithified unless they are buried by
later sedimentation.
Hooke was also concerned with the generation of global move-
ments that disturbed the strata. He suggested that these movements
were activated by earthquakes which resulted in the continents mov-
ing around, which in turn resulted in climatic alteration from place to
place. Such comments would not be out of place today. These earth-
quakes, he said, would destroy mountains and lead to the burial of
surface rocks and the exposing of buried rocks. On older, uplifted
eroded rocks he conceived younger sediments being laid on top. This
was the first explanation of how an unconformity would be produced.
We see in Hooke's Discourse a dynamic cyclical theory of the Earth,
not fully developed, that found voice through a Scottish gentleman
farmer some eighty years later. For this, and if only for this alone,
Hooke deserves greater credit and acknowledgement: his geological
ideas certainly influenced this Scottish gentleman, whose own writ-
ings laid the basis for the global theories now taken as read by geologists
and by most of the general public. Thanks to the long-standing efforts
of a few historians of geology, most notably Ellen Tan Drake, and the
celebrations that marked the tercentenary of his death, Hooke has at
last joined the pantheon of seventeenth-century scientific worthies.
LOCAL THOUGHTS ON LOCAL STRATA
While today Hooke's and Steno's ideas in stratigraphy are held as being
the first in this subdiscipline of geology, it is difficult to appreciate just
