598 proceedings of the academy of [nov., 



4. The Antigua Formation of Spencer. 



East of a line running from near Wetherill's Point to the head of 

 Willoughby Bay the surface of the island is composed of the Antigua 

 Formation (as Spencer has named it), a white chalky or marly rock 

 with harder layers which may be properly called limestone. In the 

 cane cultivations with which the island is covered from the Central 

 Plain easterly, this formation may often be recognized by a pronounced 

 blackness of the soil where the marls are encountered. They are 

 often exposed in road-cuttings, or on the hillsides by artificial diggings 

 ("marl pits") for material to be used as road metal; and where soft, 

 the dip is obscure, but where more hard the same northeasterly dip 

 is seen that was so characteristic of the tuffs and shales. As soon as 

 the harder limestone layers are encountered, they make hills with a 

 gentle easterly slope, but a steeper westerly one on the escarpment 

 side of the hill; and this harder part of the marl or the harder lime- 

 stone is often exposed upon this escarpment side of the hill in con- 

 siderable cliffs. Where the harder limestones outcrop along the 

 coast as at Wetherill Bay and Hodge's Bay along the north coast, 

 and at High Point and other places to windward along the east coast, 

 around to Willoughby Bay on the southeast coast, these harder 

 layers form sea cliffs. These harder layers, too, form in many cases 

 the capping of the hills, which are ridges with an even summit in 

 such cases. Where the dip can be seen, on such harder layers, it is 

 uniformly to the northeast, and the thickness of this Antigua for- 

 mation, as indicated by this dip, must be upwards of 1500 feet at 

 least. The harder layers have generallj^ the same organic remains, 

 and this seems to indicate (unless the formation is faulted) that 

 there are several parallel hard layers. The fossils contained in the 

 softer marls are usually corals, in a much altered and crystallized 

 condition; the crystallization being due to the deposit of carbonates 

 (as calcite and dolomite) or to silica in the form of quartz, crystals 

 of which substance are frequently seen in the marls. The harder 

 layers are often compact limestone, sometimes nearly barren of 

 fossils, at other times crowded with organic remains. The most 

 characteristic fossil in the harder layers is an Orbitoides, which has 

 been determined by T. Rupert Jones (and this determination later 

 confirmed by Dr. Lang, of the British Museum) as Orbitoides mantelli 

 Mort. This Orbitoides, in many cases, forms the bulk of the limestone, 

 and water-worn pebbles from the seashore frequently show only 

 sections of this Orbitoides with no other fossil. But in other layers 

 are found shells of oysters, pectens, and other pelecypods, while in 



