190 ME. E. WETHEEED OX IlfSOLTJBLE EESIDUES EEOM 



DESCEiPTioi;r op the Eesidiies. 



In describing the residues I shall follow the plan already adopted 

 of commencing with the Lower Limestones and proceeding 

 upwards. 



LowEE Limestones. 



i. Lower Limestone Shales. 



ISo. 1. Mostly detrital quartz-grains averaging about -001 of an 

 inch in diameter. There are also dark siliceous objects present 

 which are not entirely negative to polarized light. 



1^0. 2. Detrital quartz (Plate YIII. fig. 1), averaging about -003 

 of an inch in diameter. A few grains of felspar, tourmaline, and 

 zircon. 



Ko. 3. Detrital quartz, averaging '005 of an inch in diameter, 

 some zircon and amorphous silica, which polarizes around the edges. 



JS'o. 4. Detrital quartz averaging about "006 of an iuch in dia- 

 meter, some of the grains containing cavities. Grains of tourmaline, 

 zircon, felspar, and amorphous and chalcedonic silica are also present. 



i^o. 5. The specimens were taken from the rock which the late 

 Mr. Stoddart, some years ago, described* as the "Microzoal bed". 

 He treated the limestone with cold hydrochloric acid, and obtained 

 a residue consisting of " casts or else pseudomorphs composed of per-, 

 oxide of iron and silica." Mr. Stoddart rightly states that the casts 

 are those of the joints of Crinoids and remains of Polyzoa : but, in 

 addition, I have found those of corals. An examination of the sections 

 of the rock, under a microscope, shows that the calcareous skeleton of 

 the Corals and Polyzoa are generally preserved, and it is the portion 

 of the organism occupied during life by organic matter which has 

 been filled with oxide of iron. With the remains of Crinoids it is- 

 different, as the whole skeleton appears to be replaced by oxide of 

 iron, and that too without destroying the areolar structure charac- 

 teristic of the Echinodermata. On treating the residue left by the 

 cold acid with boiling acid the whole of the ferruginous constituents 

 disappear, and a siliceous residue remains (fig. 2). This residue 

 consists of casts of Crinoids and other organisms, chalcedonic silica, 

 detrital quartz, and a few grains of tourmaline. 



ii. Black Boclc. 



No. 1. Eesidue composed of siliceous flakes. 



Xo. 2. Detrital quartz, chalcedonic silica, a few micro-crystals, 

 and some tourmaline. 



'No. 3. Detrital c^uartz, around some of which a slight secondarj- 

 crystallization has commenced, a few grains of toui'maline and 

 zircon, and some pyrites. 



No. 4. Much detrital quartz, tourmaline, zircon, and a quantity 

 of pyrites which, when viewed by reflected light, seems, in some 

 instances, to be pseudomorphic. 



* Ann. & Mag. Xat. Hist. 3rd ser. toI. viii. p. 487. 



