190 Correspondence — Mr. J. S. Gardner. 



C(D:R:R':Bisip(Di<TJDJEiisrG:E. 



ELEVATION AND SUBSIDENCE. 

 Sir, — I have just seen the December Number of the G-kological 

 Magazine containing a short article called " The Pleistocene 

 Geology of the Firth of Tay and the Elevation and Subsidence 

 Question." The writer remarks on the depression of the land to 

 a depth of at least 500 feet during the earlier part of the Glacial 

 Period, and adds that, as the marine stratified deposits rest " upon 

 the ground moraine of the ice-sheet," whatever this may mean, it is 

 conclusively shown that when the sea sands were deposited, "the 

 ice was very greatly reduced, had retired from the coast-line, and 

 possibly disappeared altogether." He further thinks it evident that 

 this submei'gence was relatively short, and that a greater, which 

 deposited an extensive raised plain, occurred " when the glaciers 

 were in their final retreat," and deduces from these facts that "at 

 any rate the Glacial and Post-Glacial history of Scotland gives no 

 countenance to tbe theory," i.e. that additions of weight produce 

 subsidence. Original observations of fact are valuable, and any 

 inferences fairly deducible from such have a right to be tacked on, if 

 the observer pleases ; but in this case there do not appear to be any 

 new facts quoted, and certainly none that justify any approximation 

 to the sweeping assertion just cited. The continued depression of 

 the land by the accumulation of ice would naturally lead to en- 

 croachments of the sea, which would melt the ice and deposit on the 

 top of the " ground moraine," if any existed, stratified sand, or mud. 

 The Firth of Tay would, in fact, become a fiord. Why this re- 

 placement of ice by sea-water on an area should lead to the belief 

 that the thickness of ice on adjacent and more elevated areas had 

 diminished, I cannot think. Ice even in Greenland seldom reaches 

 the sea-shore, except at the heads of fiords, while an accumulating 

 ice-cap, such as the Vatna-jokul, which is 3000 miles in extent, 

 might be exerting considerable influence in the direction of depression 

 without coming near the sea. Not long since an equally valuable 

 criticism was advanced, namely, that because elevation had com- 

 menced before the disappearance of the ice-sheet, it could not have 

 been caused by it, as if an ice-cap of a thousand feet thickness or so 

 "would not get very sensibly lighter before it disappeared. 



J. Starkie Gardner. 



ON PALMOGTGLUS FLETGHERI, EDW. H. 

 Sir, — In the Quarterly Journ. Geol. Soc. for February, 1884, 

 Prof. Duncan demurs as to the identity of PaJesocydus Fletcheri with 

 Pholidophjllum tuhulatum, Schlotheim ( = PhoL (Cyathophyllum?) 

 Loveni, E. H.), chiefly on the ground that Prof. Duncan has never 

 seen in English specimens a trace of the peculiar scaly coating, 

 which covers the epitheca of Pholidophylliim. I have, amongst other 

 specimens of this coral from Dudley, sent through the kindness of 

 Mr. John Gray, of Hagley, two of the low depressed variety 



