526 Correq:)ondence — Mr. J. Smith. 



coK-iaiESi^oisrxDiEisrGE. 



FEESH-WATER OSTRACODS IN THE LOWER CARBONIFEROUS 

 SERIES OF AYRSHIRE. 



Sir. — On Friday last I found a bed of fresh-water Ostracoda, in 

 the strata exposed in the Gurdy cutting of the railway from Giifen 

 to Kilbirnie. 



The beds exposed are as follows : — 



Highest marine limestone seen in the cutting. ft. ins. 



Black shale, tough ... ... ... ... ... ... 1 8 



Dark shale 8 



Dark shale crowded with fresh-water Ostracoda ... ... 9 



Dark shale ... ... ... ... ... ... ... 1 6 



Sandstone with Stigmaria ... ... ... ... ... 3 6 



Thick bed of dark shale with abundance of marine fossils. 

 Limestone with marine fossils. 



Many of the Ostracoda are filled with pyrites, but the valves are 

 calcareous ; and they often fall otf when touched with the point of 

 a needle. The carapaces are usually white, giving the shale a sandy 

 appearance ; sometimes they are brown. They occur mostly as single 

 valves. 



I believe this is the first time that fresh-water Ostracoda have 

 been found in connection with the marine limestones of Ayrshire. 

 The position of the beds is in the upper part of the Lower Car- 

 boniferous Limestone Series of Ayrshire. 



Mr. Robert Craig has described the strata of the Gurdy cutting in 

 the Trans. Geol. Soc. Glasgow, vol. ix, p. 64. J. Smith. 



MONKLREDDING KiLWINNING, Sept. 20, 1897. 



TRINUCLEUS SETICORNIS. 

 Sir, — Mr. Marr's letter requires a final answer. "When a fossil 

 is not recorded from a certain horizon it is naturally believed 

 that it has reallj'' not been found on that horizon. It is almost 

 needless to say that when subsequent research proves an earlier 

 statement to be wrong we consider that the author of it made 

 an unavoidable mistake — unavoidable because of the imper- 

 fect knowledge of that time, but a mistake nevertheless in the 

 light of present knowledge. Such mistakes must, of course, be 

 frequent in the progress of any science, particularly in the case 

 of the range of fossils. With regard to the range of the species 

 in question, I have declined to be drawn into an argument, because 

 I find sevei-al distinct forms are included under this name by 

 difi"erent authors. F. E. Cowper Eeed. 



Cambkidge, October 4, 1897. 



A QUESTION OF NOMENCLATURE : CHEMICAL NAME FOR H2 0. 

 Sir, — In writing of the volatile constituents of an igneous magma, 

 paste, or lava, of which the gas of Hj forms the greater and most 

 important part, I do not know what term should be used in ordinary 

 parlance, as such words as water, water-gas, steam, vapour, simply 

 inqdy definite physical states of H^ 0. Now in a lava under 

 moderate pressure Hg may exist as bteam in the form of bubbles 



