392 SECTIONAL TRANSACTIONS.—C. 
except as pebbles in Cretaceous and Tertiary strata. Hornblendic granite or 
diorite has, however, been found to underlie conglomerates made up largely of 
its débris, the conglomerates being certainly not newer than early Eocene; 
this plutonic rock probably formed part of the Cretaceous floor. Good crystal- 
line schists (hornblende-schists and quartz-sericite-schists) and marble have 
also been found among unaltered strata in the basin of the River Yallahs. 
These and the serpentines which occur in the same area all appear to be of 
pre-Mesozoic age, like the similar rocks in Cuba, but their field relations have 
not been fully studied. 
An effort has been made to zone the Tertiary limestones by means of their 
foraminifera. The Yellow Limestone, recently proved by Trechmann to be of Middle 
Kocene age, contains beds full of Operculina with a few minute Dictyoconi, occasional 
beds of Alveolina, and others of a large Orthophragmina. The overlying White Lime- 
stone ranges from Upper Eocene to Upper Oligocene, the foraminiferal succession 
in ascending order being as follows: Alveolina and Dictyoconus ; Dictyoconus without 
Alveolina ; small lenticular Lepidocyclines; large Lepidocyclines (zone of Lepido- 
cyclina cf. gigas and L. undosa); Sorites. The Sorites-zone forms the Santa Cruz 
Mountains of St. Elizabeth and large tracts of Manchester. The flint-bearing, chalky, 
and globigerinal ‘ Montpelier Formation ’ of Hill lies below the Lepidocyclina undosa 
zone, but its type of sedimentation is missing from the succession in many parts of 
the island, and it seems to be a deep-water facies of the White Limestone that passes 
laterally into shallower-water mollusca-bearing beds. Hill’s ‘ Moneague Formation ’ 
certainly includes the L. wndosa zone, but its upper limit was not defined by that 
writer. Above the Moneague Formation he placed his ‘Cobre Formation’ as the 
highest division of the White Limestone, but the type section in the Cobre gorge 
contains an abundance of Dictyoconus and an absence of Sorites in the lower part of 
the gorge, an indication that the strata lie below the LZ. wndosa zone and below the 
Moneague beds. The base of the White Limestone is of variable horizon, sometimes 
passing up conformably from the Yellow Limestone, sometimes overlapping on to 
older rocks against the shores of a subsiding land. 
An account is given of the igneous rocks. The latest intrusions appear to 
be of Upper Eocene age. ‘the Low Layton ‘Extinct Volcano,’ possibly of 
Oligocene age, was found to contain many ‘ pillows’ of highly vesicular lava, the 
pillows being sometimes truncated, and the vesicles being usually arranged 
inside the pillows in well-defined concentric zones. 
24, Dr. C. A. Matiry.—A Reconnaissance Geological Survey of the 
Cayman Islands, British West Indies. 
The Cayman Islands, a dependency of Jamaica, consist of the two smaller 
islands of Cayman Brac and Little Cayman and a larger island, about sixty 
miles from the Lesser Caymans, known as Grand Cayman. They are the only 
projecting peaks of the submarine Cayman Ridge that extend from the Sierra 
Maestra range of Cuba to the Misteriosa Bank in the direction of British Hon- 
duras. Cayman Brac rises to 130 cr 140 feet above the sea at its eastern end, 
but the other islands do not exceed 50 or 60 feet. The submarine slopes round 
the individual islands are steep. Within eighteen miles of the shores of Grand 
Cayman a depth of over 20,000 feet is attained (Bartlett Deep). 
The geology of the group has hitherto been practically unknown. The 
present survey has shown that each island contains limestones of two different 
ages, an older limestone (Bluff Limestone) closely resembling the white limestone 
of Jamaica, and forming an inner and more elevated platform, and a younger 
calcareous formation (Ironshore Limestone) forming an outer and lower coastal 
platform, the seaward edge of which is covered in many parts by modern shore 
deposits of coral-sand and coral-shingle thrown up by winds, storms, and hurri- 
canes. Out at sea are coral reefs that surround the islands of Grand Cayman 
and Little Cayman almost completely, and occur to a lesser extent around 
Cayman Brac. 
The Bluff Limestone is a massive white recrystallised limestone, with its fossils 
so poorly preserved as casts that usually they cannot be determined specifically. 
Among them occur mollusca (chiefly gasteropods), reef-building corals, nullipores 
and foraminifera. At the Bluff of Cayman Brac is a bed full of large Lepidocyclines 
which have a close resemblance to those of the zone of Lepidocyclina gigas and 
L. undesa found in the middle beds of the white limestone of Jamaica, and occurring 
