326 Mr. Weaver's Geological Observations on 



compact brown ironstone or haematite. It may appear almost superfluous 

 to remark, that iron enters also largely into the composition of the trap. 

 Generally speaking, when the sandstone, limestone, or slate-clay become 

 partially disintegrated by weathering, they acquire a stained appearance, 

 from the oxidation of the ferruginous particles diffused through their sub- 

 stance ; and the same cause produces a similar effect on the trap. 



§ 9. The stratified transition beds, now described, abound, in particular 

 parts, in the remains of organized bodies, more especially when they are 

 thinly stratified with each other, or when the sandstone is adjacent to the 

 calcareous beds. But many of the sandstone strata, when nearly continuous, 

 appear mostly, if not entirely, free from them. 



The following are the organic remains which I have observed ; but many 

 of them are frequently so interwoven and entangled with each other, and with 

 the substance of the including rock, often appearing only as partial impres- 

 sions or casts, that a reference to distinct species becomes in most cases nearly 

 impracticable. I confine myself therefore, in a great measure, to general 

 indications. 



The only remains of vertebrated animals that I have met with, are bones 

 and a tooth, apparently of fish ; the former in Whitefield quarry and at Skeay's 

 grove, and the latter in Skeay's grove alone *. 



Of the crustaceous animals, trilobites frequently occur, being referable to 

 four distinct species. Of these, the most common is the Asaphus caudatus 

 of M. Brongniart (Histoire Naturelle des Trilobites, PI. II. fig. 4.) ; which 

 is also often found in the transition tract of North Gloucestershire, Here- 

 fordshire, and Worcestershire. In the Tortworth district, I have never met 

 with a specimen of this trilobite so perfect, as to exhibit at one view the entire 

 form of the animal : but the head, body, and caudal termination of different 

 specimens (though the last is very seldom distinctly displayed), fully establish, 

 when taken together, the identity of the species. 



The next species, which is also not of uncommon occurrence, is referable 

 to the Calymene variolaris (Brongniart, PI. I. fig. 3.) ; but of this I have never 

 met with a complete specimen. The part most generally exhibited to view 

 is the post-abdomen only; the head is much more rarely visible ; and these two 

 parts are found separate and detached from each other, the abdominal portion 

 of the body appearing to be wholly wanting f . The specimens of the head of 



* I know of only one other instance in which the remains of fish have been noticed in a tran- 

 sition tract ; that, namely, of the impressions in the transition slate of the Blattenberg, near 

 Glarus, in Switzerland. 



f The post-abdomen in this species is distinguished by a single row of five small tubercles, of an 



