48 Mr. Brockbank on 



Levenshulme limestones. It will be seen that Mr. Sorby's 

 description falls very short of the reality, if we are to take 

 the Levenshulme limestones to represent those of Ardwick. 



In communicating my first notes on the Levenshulme 

 railway section to the Society last year, I made especial 

 reference to the circular greenish spots which we had found 

 everywhere present throughout the Triassic, Permian, and 

 Carboniferous shales, sandstones, marls, and limestones, and 

 which went by the name of " fish eyes." I stated that it 

 would^form a very interesting subject for enquiry, and I 

 believed it would be found that these green spots were 

 caused by the presence of Entomostraca. The "fish eyes" 

 puzzle was ever before me, and I have been engaged upon 

 it since. The solution of this question in the mottled lime- 

 stones will, I think, govern all the rest ; for they all appear 

 to me to have similar conditions and appearances through- 

 out the section from Trias to Coal Measures. 



The whole of the Levenshulme limestones are more or 

 less mottled. The basis colour is always grey, tinged pink 

 with hematite; and this very sensitive pink colour is so 

 readily discharged by an acid, that it forms a very delicate 

 test if we can only follow out its indications. I very soon 

 came to the conclusion that the cause of the greenish 

 mottlings had a connection with animal life. In addition to 

 the green mottlings, however, there were also smaller deep 

 purple ones. A very simple examination of these tiny circles 

 shewed them to be Spirorbis shells, cut through in all 

 directions, this giving a dark purple mottling to every one 

 of the limestones. In the upper beds the Spirorbis is less 

 abundant, but in the middle beds the limestone is almost 

 made up of its tiny shells. There is a polished sample of 

 marble on the table from a bed in group No. 2, which shews 

 about 300 Spirorbis shells in the square inch, giving the 

 amazing number of 90,000 in one cubic inch. The mass of 

 limestone is thus nearly built up of the remains of this 



