12
paleocurrent and paleogeographic analyses. In dealing with ancient deposits, the authors' preoccupations are mainly with stratigraphic documentation.
However, some glimmerings of fl uvial sedimento�
logy do creep in. Dana wrote "in the alluvial deposits
from a flood the little layer is begun with a relatively
rapid rate of deposition and finished with a slower,
as the fl ood declines, and hence its upper and lower
portions will differ as to coarseness and density''.
Here, we have the first recognition of the cyclic nature of fl ood deposits. Dana also provided a good
description of the shape and development of transverse sand bars, based on the work of General G.K.
Warren, another of the US Army topographers, on
the Mississippi River. Geikie wrote:
"The deposit of alluvium on river beds is characteristically ·
shown by the accumulation of sand or shingle at the concave side of each sharp bend of a river course. While the
main upper current is maldng a more rapid sweep around
the opposite bank) undercurrents pass across to the inner
side of the curve and drop their freight of loose detritus
which, when laid bare in dry weather, forms the familiar
sand�bank or shingle beach."
This is an eminently clear description of the helical flow patterns that occur on river meanders, and
of the point-bar deposits that result. It remains only
to provide the idea of decreasing competency and
sediment sor�ing up the point-bar slope to arrive at
the finirtg-upWard model. However, this was not to
come for another 80 years.
In spite of the general acceptance of the principle
of uniformitarianism, these excellent observ�tions
on modern fl uvial environments were not, at this
time, being applied to interpretations of ancient
rock successions. Copious descriptions of the lithology, fauna, and flora of such nonmarine units as the
Old Red Sandstone were given by Dana and Geikie,
but environmental and paleogeographic interpretations were limited to general statements concerning
the deposition of such rocks in lakes or "inland
seas". Their general nonmarine nature was recognized, but furth€:r interpretations did not proceed
beyond such statements as this, from Dana, concerning the Triassic of the Appalachians:
"The mud-cracks, raindrop-impressions and footprints -
these show, wherever they occur, that the layer was for the
time a half�emerged mud-flat or sand-flat; and, as they
extend through much of the rock) there is evidence that the
layers in general were not formed in deep water ... The
occurrence ... of coarse conglomerate, some of the stones
of which are very large and of a coarse l
waters pouring violently down this valley."
Historical Background
Dana also thought that floating ice was "concerned in part of the deposition". A detailed report
on these same rocks by the geographer and geomorphologist W.M. Davis (l898a) included a detailed
discussion of the various possible environments
in which they could have formed, including tidal,
lacustrine, fl uvial, glacial, or eolian setings. It is a
fine example of sedimentological reasoning, in
which modern analogs are clearly appealed to. For
example:
"The Pre� Triassic peneplain might have been warped so as
to alter the action of the quiescent old rivers that had
before flowed across it ... Such a change would set the
streams to eroding in their steepened courses, and to de�
positing where their load increased above their ability of
transportation ... The heavy accumulation of river-borne
waste on the broad plains of California, or of the Indo�
Gangetic depression all agree in testifying that rivers may
form extensive stratified deposits, and that the deposits
may be fine as well as coarse. They are characteristically
crossbedded and variable, and they may frequently contain rain-pitted or sun�cracked layers."
However, Davis was a cautious individual. He
concluded:
"Penck has suggested the name 'continental' for deposits
formed on la:nd areas, whether in lakes, by rivers, by winds,
under the creeping action of waste slopes, or under all
these conditions combined. This term seems more appli�
cable thari any other to -the Triassic deposits of Connecticut. It withdraws them from necessary association with a
marine orig�n, for which there is no sufficient evidence,
and at the same time it avoids what is today an impossible
task - that of assigning a particular origin to one or another member of the formation.''
The last sentence is revealing, for it shows that
application of the growing body of knowledge about
modern environments to sedimentological problems was still very much in its. infancy. Davis was
somewhat more self-confident in his fluvial interpretations of the Tertiary strata of the Rocky Mountains, pubished only 2 years later (Davis 1900).
At about this time, Davis (1898b, 1899) also made
a major contribution to fl uvial geomorphology with
his classifi cation of rivers according to their stage of
development in the erosion cycle as youthful, mature, and old, and he recognized and described rivers
of braided and meandering character.
A rather more advanced level of interpretation of
fluvial sediments was given earlier by Medlicott and
Blanford (1879), but their observations were not
widely applied for some years. They described the
Siwalik · Formation of the Himalayas, compared it
with the "Molasse" of Switzerland and with modern
alluvium, as follows:
paleocurrent and paleogeographic analyses. In dealing with ancient deposits, the authors' preoccupations are mainly with stratigraphic documentation.
However, some glimmerings of fl uvial sedimento�
logy do creep in. Dana wrote "in the alluvial deposits
from a flood the little layer is begun with a relatively
rapid rate of deposition and finished with a slower,
as the fl ood declines, and hence its upper and lower
portions will differ as to coarseness and density''.
Here, we have the first recognition of the cyclic nature of fl ood deposits. Dana also provided a good
description of the shape and development of transverse sand bars, based on the work of General G.K.
Warren, another of the US Army topographers, on
the Mississippi River. Geikie wrote:
"The deposit of alluvium on river beds is characteristically ·
shown by the accumulation of sand or shingle at the concave side of each sharp bend of a river course. While the
main upper current is maldng a more rapid sweep around
the opposite bank) undercurrents pass across to the inner
side of the curve and drop their freight of loose detritus
which, when laid bare in dry weather, forms the familiar
sand�bank or shingle beach."
This is an eminently clear description of the helical flow patterns that occur on river meanders, and
of the point-bar deposits that result. It remains only
to provide the idea of decreasing competency and
sediment sor�ing up the point-bar slope to arrive at
the finirtg-upWard model. However, this was not to
come for another 80 years.
In spite of the general acceptance of the principle
of uniformitarianism, these excellent observ�tions
on modern fl uvial environments were not, at this
time, being applied to interpretations of ancient
rock successions. Copious descriptions of the lithology, fauna, and flora of such nonmarine units as the
Old Red Sandstone were given by Dana and Geikie,
but environmental and paleogeographic interpretations were limited to general statements concerning
the deposition of such rocks in lakes or "inland
seas". Their general nonmarine nature was recognized, but furth€:r interpretations did not proceed
beyond such statements as this, from Dana, concerning the Triassic of the Appalachians:
"The mud-cracks, raindrop-impressions and footprints -
these show, wherever they occur, that the layer was for the
time a half�emerged mud-flat or sand-flat; and, as they
extend through much of the rock) there is evidence that the
layers in general were not formed in deep water ... The
occurrence ... of coarse conglomerate, some of the stones
of which are very large and of a coarse l
waters pouring violently down this valley."
Historical Background
Dana also thought that floating ice was "concerned in part of the deposition". A detailed report
on these same rocks by the geographer and geomorphologist W.M. Davis (l898a) included a detailed
discussion of the various possible environments
in which they could have formed, including tidal,
lacustrine, fl uvial, glacial, or eolian setings. It is a
fine example of sedimentological reasoning, in
which modern analogs are clearly appealed to. For
example:
"The Pre� Triassic peneplain might have been warped so as
to alter the action of the quiescent old rivers that had
before flowed across it ... Such a change would set the
streams to eroding in their steepened courses, and to de�
positing where their load increased above their ability of
transportation ... The heavy accumulation of river-borne
waste on the broad plains of California, or of the Indo�
Gangetic depression all agree in testifying that rivers may
form extensive stratified deposits, and that the deposits
may be fine as well as coarse. They are characteristically
crossbedded and variable, and they may frequently contain rain-pitted or sun�cracked layers."
However, Davis was a cautious individual. He
concluded:
"Penck has suggested the name 'continental' for deposits
formed on la:nd areas, whether in lakes, by rivers, by winds,
under the creeping action of waste slopes, or under all
these conditions combined. This term seems more appli�
cable thari any other to -the Triassic deposits of Connecticut. It withdraws them from necessary association with a
marine orig�n, for which there is no sufficient evidence,
and at the same time it avoids what is today an impossible
task - that of assigning a particular origin to one or another member of the formation.''
The last sentence is revealing, for it shows that
application of the growing body of knowledge about
modern environments to sedimentological problems was still very much in its. infancy. Davis was
somewhat more self-confident in his fluvial interpretations of the Tertiary strata of the Rocky Mountains, pubished only 2 years later (Davis 1900).
At about this time, Davis (1898b, 1899) also made
a major contribution to fl uvial geomorphology with
his classifi cation of rivers according to their stage of
development in the erosion cycle as youthful, mature, and old, and he recognized and described rivers
of braided and meandering character.
A rather more advanced level of interpretation of
fluvial sediments was given earlier by Medlicott and
Blanford (1879), but their observations were not
widely applied for some years. They described the
Siwalik · Formation of the Himalayas, compared it
with the "Molasse" of Switzerland and with modern
alluvium, as follows: