20 A NEW FLORA OF 



the fern Neuropteris Suttoniana ; and also Caulerpa selagimides, 

 and other obscure plant-remains, which have been regarded as 

 fucoids. These associated organisms indicate estuarine conditions. 



2. Compact limestone, which is earthy or crystalline, brown, 

 grey, mottled or ribboned, and slaty in the bottom beds. The 

 crystalline is chiefly carbonate of lime, but the earthy sometimes 

 contains as much as 44*9 per cent, of carbonate of magnesia. It 

 has a thickness of from 150 feet to 200 feet, but contains few 

 fossils, only eighteen species having been found in it : it appears, 

 however, to have been throughout a pelagic deposit. 



3. Possiliferous limestone, which has a thickness of about 

 150 feet, is generally light yellow, compact or crystalline, with 

 little appearance of stratification. It is so rich in fossils that 

 about ninety species have been found in it, indicating a pelagic 

 deposit. 



4. Concretionary and pseudo-brecciated limestones, are about 

 150 feet thick, mostly of a light yellow colour, and containing 

 corals and mollusks, indicating generally pelagic conditions ; but 

 in some laminated or slaty beds fishes have been found in consi- 

 derable numbers, of the genera Pal<Boniscus and Acrolepis, accom- 

 panied with a calamite, and with other plants supposed to be 

 fucoids. 



5. Crystalline, compact, and oolitic limestone, which is often 

 laminated, and sometimes ripple-marked. Corals and Brachio- 

 pods are absent, but it contains species of Myalina and Schizodus, 

 which point to shore or shallow water. It is about 100 feet in 

 thickness. 



The organisms of the Magnesian Limestone bring it into close 

 relationship with the Carboniferous system, of which it properly 

 ranks as a group or formation. Sedgwick, in 1828, pointed out 

 this alliance, and further researches have confirmed his view : 

 Mr. Kirkby has shown that fifteen species of animals were com- 

 mon to the Mountain Limestone and the Magnesian Limestone 



