20-1 BEOWELL AND EIEKBY OX MAGNESIAN LIMESTONE 



search might have revealed it elsewhere. Still, supposing it to 

 he really confined to the single pool in which it was found, it 

 only presents a parallel to the similar partial distribution of 

 Crustacea, &c. For example, one or two pools swarmed with 

 Mysis vulgaris, no other animal being visible ; another was filled 

 in like manner with myriads of a little prawn- — Palmmon varians, 

 while others seemed to be entirely devoted to a gasteropodous 

 mollusc — Rissoa TJhm. 



XXIII. — On the Chemical Composition of various Beds of the 

 Magnesian Limestone and Associated Permian Rocks of Durham. 

 Ey E. J. J. Browell and James "W. Xiekby. 



Although hundreds of analyses of samples from the Magnesian 

 Limestone formation of tbis district have been made at various 

 times, and some of them, both by myself and others, have been 

 published in various forms, there has, I believe, never been yet 

 published anything approaching to a complete Series, represent- 

 ing the various sub-formations and beds known to geologists. 

 A desire for something of the kind having been often expressed 

 by many of our local naturalists, I undertook the chemical 

 examination of a Series collected and arranged by Mr. J. "W. 

 Xirkby. It was intended at the outset to make the analyses 

 more detailed and elaborate than I have ultimately done, but the 

 number of analyses required made this departure from the ori- 

 ginal plan necessary ; and after all, though more minute analyses 

 would look more imposing, they would scarcely be of more in- 

 terest to the geologist, in whose eyes the chief interest will con- 

 sist in the relation of the carbonates of lime and magnesia to 

 each other, and to the total amount of other matters (clay, &c.) 

 E. J. J. B. 



~We describe the samples analysed in the geological sequence 

 of the strata to which they belong, commencing with the lowest. 



