vol. 54.] on the globigerina-maels, etc., oe baebados. 547 



ly. bowmanston and othek localities where similar 

 Rocks occur. 



Bowmanston is situate on a plateau of coral-rock, the hous 

 being at an altitude of 620 feet above the sea. Many years ago a 

 shaft was sunk here to reach water, and at a depth of about 260 

 feet the sinking dropped through the roof of an underground water- 

 course, in which the average water-level is 360 feet above the sea, 

 or 280 feet from the surface. 



The lower portion of this shaft and the cavern into which it opens 

 have been examined by us on several occasions, and a number of 

 rock-samples obtained. The lower part of the cavern is cut through 

 an ochreous-yellow G(ohigerma-m.aTl much resembling that which 

 occurs on Bissex Hill ; above this there is a Globigerina-limeatone 

 forming a fairly hard rock, containing included fragments of chalk 

 and of indurated radiolarian earth derived from the Oceanic Series. 

 This rock is similar to the limestone that occurs near the summit of 

 Bissex Hill, and on ascending the sides of the cavern it is found to 

 pass into a limestone which is destitute of Glohigerince, but contains 

 a great number of Amphistegince, together with some Bigenerince, 

 Nodosarice, Textularice, and other foramiaifera. The calcareous 

 alga Litliothamnium and fragments of echinoderms are frequently 

 present. The same Amphistegina-limestoue occurs at the bottom of 

 the shaft, and continues upward for 10 or 12 feet, but at a level of 

 about 410 feet above the sea it gradually passes into true coral- 

 rock. 



The sequence of rocks below Bowmanston therefore coincides 

 with, and confirms, that observed on and near Bissex Hiil. There is 

 no means of ascertaining how much Globigerina-m.'dil lies below the 

 floor of the cavern, but its existence there is sufficient to show that 

 the outlier of Bissex Hill is part of a formation which had a con- 

 siderable extension. 



Many borings have been made through the coral-rock capping of 

 the island, and these show that between the Oceanic or the Scotland 

 Beds and the basal reef-rock there is generally a foraminiferal mud. 

 This mud sometimes contains a very few thick-tested Globigerince, 

 similar to those of Bissex Hill, and inclusions of the Oceanic Beds 

 and of clays possibly derived from the Scotland Beds are not un- 

 common. Thick-tested Glohigerince occur very sparingly also in lime - 

 stones obtained from the bottom of shafts sunk through the coral at 

 Plumtree GruUy, on Farmer's Estate, at levels of 684, 693, and 706 

 feet, and also in the earth from an underground cave at Bock 

 Dundo at a level of 2Q2 feet. The first three of these are coral-reef 

 rocks containing abundant Amphistegince and a great variety of 

 other organisms, including many echinoderm-fragments. They also 

 show the presence of Liihothamnium in considerable quantity, while 

 fair-sized inclusions from the rocks of the Oceanic Series are common. 

 The earth from Bock Dundo is soft, and contains inclusions of 

 comminuted radiolaria. 



