CHAPTER XIII.
66
THE STORY OF THE CRAGS,"
Meaning of the term "crag "-Where these beds are found-
Their number-The Pliocene period-The Coralline, Red,
and Norwich Crags-Suffolk the bed of a tolerably deep sea
-Fauna of the Coralline Crag sea-Ancient sea urchins-
Where now living-Time since Coralline Crag was formed
-Abundance of mollusca in Coralline Crag sea—'
-The As-
tartes-Pectunculus-Cyprina-Number of species of mol-
lusca - An ancient sea-bed, and what it teaches - No
"dredging" required - "Sea Mats"- Fascicularia - Ex-
tremes in Coralline Crag sea-Marine currents-The oldest
crag-Physical conditions of Pliocene period-Migration of
mollusca southerly-Coralline Crag shells in West Indies-
Ditto in Mediterranean-Thickness of Coralline Crag-How
formed The Red Crag-Origin of name-Denudations of
Coralline Crag previous to it-An ancient land surface in
Suffolk and Norfolk-How the "coprolite" beds were formed
- Mollusca of the Red Crag "Southern " forms -
"Northern" ditto--Refrigeration of climature--Corals--Cowrie
shells-False current bedding in Red Crag-Physical geo-
graphy of ditto-The chalk of Norfolk-A shallow estuary
over site of Norwich-Evidence of river communication-The
Norwich Crag-Its fluvio-marine character-Difference in
fossils from previous crags-Abundance of littoral shells-
Tellina-Mactra- Cerithium - Fresh-water shells - Pla-
norbis, Paludina - Lymnea, &c.-Land-snails -Census of
Norwich crag-Ancient land-animals in Norfolk-The Al-
deby Crag-Its fossils-Increase of "Northerly" mollusca
-Evidence of rigorous climate-The Upper Norwich Crag,
and its lessons-Pliocene and Pleistocene periods-Analy-
zation of shells of crags-Number of extinct species in ditto
-The Belgium crags-The " Box-stones" of Suffolk-Their
origin-Evidence of a broken-up deposit-Pliocene strata in
Sicily-English shells in ditto-How they came there-
Evidence of volcanic disturbance-Formation of Mount Etna
-Height of Pliocene beds on its flanks-Refrigeration of
climate in northern hemisphere-Preparation for the long
Arctic winter-The introduction of the Glacial epoch 222-237