IN THEIR ROLE AS WORLD-BUILDERS. 



is for a large area covered with an exposure of this zone (the- 

 41 Park " beds), and one cannot walk without crushing vast 

 agglomerated masses of Nummulites laevigatas, extending for 

 miles and occupying broad areas between tide-marks. 



Off the extremity of Selsey Bill lies the extensive reef known 

 as "The Mixon." It is exposed at low tide, and is then found 

 to be a limestone principally composed of one species of fora- 

 minifer, Alveolina Boscii Def ranee. Other species (notably a large 

 alveoliniform Jliliolina, Nummulites, and a large Polymorphina) 

 are to be found in the rock, but this is dominant (PL 2, fig. 2). 

 Alveolina Boscii, which has built up enormous areas of limestone 

 extending across Southern Europe to the Himalayas, is still in 

 existence to-day, and is now forming similar deposits off many- 

 tropical shores. The Selsey specimens the only ones to be found 

 in Great Britain are indistinguishable from those to be dredged 

 in shallow water to-day, off the Great Barrier Reef of Queensland 

 and in many other places (24). 



At Stubbington and its neighbourhood, in Hampshire, smaller 

 types of Nummulites, viz. Nummulites elegans and JV. variolaria r 

 are to be found in similar abundance. 



Turning to the Continent, we find these Nummulitic and 

 Alveoline limestones developed to an incredible extent. With 

 interruptions here and there, they spread in a broad band across- 

 Europe, Asia and Northern Africa to the Himalayas, attaining 

 in many places a thickness of several thousand feet (PI. 2, fig. 3). 

 The species vary with the zone and locality, but, as a rule, the- 

 whole rock is built up of their more or less perfect remains, and 

 undeft the microscope the very debris in the interstices of perfect 

 specimens is found to consist of their comminuted remains- 

 (Pl. 2, fig. 4 and PI. 3, fig. 1). 



Among the more familiar instances of Nummulitic limestone- 

 may be mentioned the Pyramids of Egypt, which are built of 

 limestone quarried in the neighbouring Mokattam Hills, largely 

 composed of a single species of Nummulite N. Gizehensis (Ehren- 

 berg). We illustrate in Plate 3, fig. 1 a section through a micro- 

 spheric specimen of this Nummulite, one of a series collected for us 

 by Mrs. A. M. King, F.R.M.S. The peculiarity of these remains 

 struck the geographer Strabo, who accounts for their presence in 

 the limestone by asserting that they were the petrified remains 

 of lentils from the rations of the ancients who built the 



