IV GLACIATI

Relativ

ciers

diver

land

large

Deni

nortl

man

of S

joine

nortl

clude

in th

side

Meck

III GLACIATI

Less e
II;
the 1
[The
pear

the c
glaci

They

than

nor

youn

the

and

corre

II GLACIATIC

The mo
unite

and

tendi

Than

"Old

clay"

to th

tains,

sprea

Russi

join

"Old,

most

I GLACIATIC

The le
basin
ing of

man

and
Britis

(1909
find t
zian

lin a

many equiv the G

2. PERI-ALPINE TIME STANDARDS OF PENCK AND BRÜCKNER, AS
INTERPRETED BY DEPERET

Adoption of Theory of four glacial Advances

We may now give an abstract from the observations of Depéret (19181921) in their points of agreement and disagreement with the classic observations of Penck and Brückner (1901-1909). We give a fuller exposition of Depéret's work, beginning on page 422 of the present paper. The square brackets [] indicate interpolations or comments by the present authors.

First, it is interesting to observe that Depéret and Mayet adopt the theory of four glacial advances, maintained by Penck and Brückner, in Europe. We refer to two recent papers by one of Depéret's former students and present colleagues, Dr. Lucien Mayet, of Lyons (1921.1, 1921.2), from which we may make extensive citations, since he has set forth the Penck and the Depéret standards with the clearness, precision, and brevity characteristic of French scientific writers in general.

As Mayet observes (1921.2, page 482), it is not necessary to review the work of glaciologists of the last half century-for example, the publications of Falsan and Chantre, who limited the Alpine glaciers to a single great extension, in contrast to the pioneer, Geikie, who maintained six glacial periods and five interglacial phases. One of the distinguished French paleontologists, Marcellin Boule (1921.1), recognizes only three main glacial periods, the first of which is placed in Pliocene time (see Table VIII).

The

The researches of Du Pasquier, of Penck and Brückner, of Depéret, and of Kilian on the peri-Alpine region (see figure 1) relate to the fluvio-glacial complexes, their morainal formations (rallum, amphi théâtres, etcetera), their layers of transitional alluvium (cônes de transition et terrasses constituant celles-ci). In the valleys of this same peri-Alpine zone one observes a self-staged series of terraces. highest above the present stream-bed belong to the external moraines (those most remote from the central Alpine massif), which mark the maximum of glacial extension and are the most ancient; also the lowest terraces, which approach most closely the actual level of the existing rivers and are related to the internal moraines (that is, moraines within the preceding, nearer the central Alpine massif), which testify to a less extension of the glaciers and are more recent in age. Similar observations may be made, with perhaps even more precision, in certain valleys of the Pyrenees.

Vallon dale; amphithéâters = cirques.

FIGURE 1.-Map of Central and Southern European Glaciations

One may observe, moreover, four sheets or deposits of gravel (nappes de cailloutis) standing at four different levels and related to four distinct morainal formations, which are sometimes separated by considerable spaces that is, by notable differences of altitude. These four deposits of gravel (nappes de cailloutis) correspond to four different glaciations (alluvionnement glaciaire). During the first phase of each interglacial recession period there is produced an erosion (creusement), more or less intense, but always rapid, by the abundant water-floods born in the fountain of ice and establishing their stream-bed in the glacial pebbles (cailloutis glaciaire).

Terraces

On either side of the glacial stream, against the declivity of the valley, there may persist a part of the glacial layer not encroached upon and not. transported by the stream. Thus is constituted the terrace, a witness to the topographic surface built up in course of the preceding glaciation and connected with the moraines of the same glaciation. For example, as we ascend the river, the terraces are related:

(a) to the outer moraines of GLACIATION II, the terraces at levels of 50-60 meters;

(b) to the intermediate moraines of GLACIATION III, the terraces at levels of 35 meters;

(e) to the inner moraines of GLACIATION IV, the terraces at levels of 18-32

meters.

These altitudes in meters (18-60) are calculated above the present stream or river level (thalweg actuel) and in the broad valleys, farther down stream than declivities, often very steep, of cones of glacial transition. From these terrace altitudes and moraines Depéret makes the following generalization: "A chaque glaciation correspond donc une valeur differente du creusement de la vallée des cours d'eaux issus des glaciers de cette période." To each glaciation corresponds the distinctive. level of erosion of the valley produced by the occurrence of water issuing from the glaciers of the corresponding period. There is thus placed in evidence to the glaciologists of the peri-Alpine region a collection of valuable data for the division of the Quaternary Glacial Epoch, which includes the large part of the Pleistocene of Europe. Penck and Brückner in their classic work (1909.1) have given to the four great phases of extension of the glaciers, the FOUR GLACIATIONS, the following names, which we may refer to in their descending geologic order:

Postglacial Period

Behind the Würm moraines there occurs a limited number of morainal formations, moraines stadiaires of stadial or substage rank and not