486 



The Museum Gazette 



ON HORIZONTALLY RIDGED TUFA. 

 By Dr. G. Abbott. 



The specimen shown in the appended illustration is a piece 

 of tufa from the Bath oolite, and is about one-third natural 

 size. It shows very clearly certain horizontal ridges, of which 



Tufa showing Horizontal Ridges. 



I find it difficult to get any explanation ; they are, however, 

 not uncommon, for not only are they to be found on the 

 surface of fissures, as in this case, but also both on stalactites, 

 stalagmites, and on the tufa of sloping surfaces of limestone 

 caves. They are always nearly if not quite horizontal, their 

 two surfaces are frequently unequal, so that a cross section is 

 not unlike the teeth of a coarse saw. Apparently they are not 

 due to any secondary change, like the segregation banding in 

 weathered mortar, but are more probably due to some initial 

 but unrecognised force which may exist in lime. I should 

 be glad to know others' views and see photographs of similar 

 specimens (which would be returned). — G. Abbott, F.G.S., 

 2, Queen's Road, Tunbridge Wells, Kent. 



