Geology of the Bermudas. 437 



"The arenaceous forms are not well preserved. There is a con- 

 siderable amount of debris, and some fairly good specimens of 

 Clavulina angularis, d'Orb., have been found." 



VI. Some Recent Evidence of Submergence. 



(1) Phosphorite Rock from Manhattan Shoal (PI. XXIII, Fig. 2).— 

 In the Museum at Hamilton there is a large block of red rock from 

 the Manhattan Shoal, probably a core from a hole made in blasting 

 the rock for deepening the navigation channel in 1847. It came 

 from a depth of 18 feet. If this were below O.D. it would be from 

 4 feet in the rock, which is probably the depth, more or less, of this 

 interesting formation. Mr. L. L. Mowbray has kindly permitted me 

 to sectionize the material and to have a penological report inserted in 

 this paper. 



Mr. Russell F. Gwinnell, B.Sc, F.G.S., A.R.C.S., reports as 

 follows : — 



" This is a hard rock which does not effervesce on treatment with cold 

 concentrated H CI. Generally brown-red in colour, it appears in the 

 hand-specimens to consist mainly of small spherical and ellipsoidal 

 bodies together with a few subangular fragments, bound together 

 by a cement which does not rill up the interspaces between the round 

 bodies. There is no apparent striking difference in colour or hardness 

 between any of the constituents of the rock (PI. XXIII, Fig. 2). 



" Under the microscope the round bodies are seen to be of various 

 sizes, from a diameter of about 1*5 mm. down to perhaps 0*1 mm. ; 

 a great many are approximately - 4 or 05 mm. in diameter. They 

 show a certain amount of concentric zoning of colour, often with 

 a lighter interior and darker border ; otherwise there is no well-defined 

 structure (as is frequently seen in oolitic and pisolitic grains), but 

 the whole body contains numerous irregular fragments scattered 

 promiscuously throughout. This structure is strongly suggestive of 

 coprolites. The rounded bodies are non-pleochroic and isotropic. All 

 the characters, so far, suggest the material as being phosphorite, the 

 amorphous variety of calcium phosphate ('apatite ' when crystalline) 

 having been originally produced as coprolites, that is, the excrement 

 of such animals as fishes or birds. For this reason, chemical tests for 

 phosphorus were kindly made for me by Mr. T. Eastwood, A.R.C.S., 

 and the presence of this element was clearly indicated. The rock 

 also contains a few small subangular pieces of quartz and calcite. 



"Encrusting the rounded bodies (which will now be spoken of as 

 ' guano ' or coprolites) is a thin layer of a transparent material, 

 nearly colourless in thin section. This material also occurs apparently 

 inside a coprolite, but this appearance may be due to the invagination 

 of the surface of the coprolite. In polarized light this encrusting 

 material is seen to be anisotropic, formed of fibres arranged normally 

 to the surface which is encrusted. The birefringence is very low, 

 but the refraction decidedly high. The fibres give straight extinction 

 between crossed nicols, and a determination of the optical sign proves 

 the material to be negative. These optical characters, together with 

 the mode of occurrence, leave no room for doubt that this encrusting 



