UPTHRUST MARINE MUDS 273 



As regards the geological age of the raised marine muds, it may be added that 

 a considerable amount of fragments of algce were distributed throughout the deposit, 

 and these show little signs of decomposition or alteration. Mi-. Hallman comments 

 on the fact that " at one point there are remains of a small chitinous avicularium, 

 attached to one of the specimens of Lepralia." The fact, therefore, that the 

 animal matter has not yet been lost is proof of the comparatively recent age of 

 this deposit. 



These observations clearly point to the elevated muds belonging to very recent 

 geological time, and if the ice domes in the neighbouring areas are due to settle- 

 ment, consequent on withdrawal of the ocean, the movement is actually still in 

 progress. On the whole, we strongly favour the view that the marine muds near 

 Backstairs Passage owe their elevation to upthrust by glacial action. A few of the 

 larger marine organisms of this deposit are shown here on Plate LXXXVIII. 



2. Dry Valley. About 148 miles southerly from the "raised muds" just de- 

 scribed, one of us (R. E. Priestley), in company with Bertram Armytage, discovered 

 a raised beach at Dry Valley near New Harbour. This beach consisted of dark 

 gritty sand containing numerous entire valves of Pecten Colbecki, up to elevations of 

 about 50 feet above sea-level, and at a distance of several hundreds of yards in- 

 land from the present shore. Associated in abundance with these pectens was an 

 Anatina ; two double-valved shells of another species of bivalve {Lima) were obtained 

 by digging several inches below the surface of this sand. Both the pecten and 

 Anatina have extremely fragile shells, yet hundreds of valves, of the pecten especi- 

 ally, were practically intact, ears and all being perfectly preserved. They have 

 a very recent aspect. The only reasonable explanation of the occurrence of such 

 vast numbers of delicate and well-preserved shells in this deposit is that it is a 

 genuine raised beach. It is obvious that in this case also, as at Mount Larsen, an 

 elevation of more than 50 feet is implied. Such deposits of pecten and Anatina 

 shells might have formed at depths like those in Backdoor Bay near our winter 

 quarters at Cape Royds, where we used to dredge up such shells from depths of 10 

 fathoms. Perhaps, therefore, these shells indicate a recent elevation of this part of 

 the coast of possibly as much as 100 feet. Some of the marine organisms from these 

 deposits are figured on Plate LXXXIX. 



3. Backdoor Bay. The first spot discovered by Bertram Armytage on the 

 eastern shores of Backdoor Bay, 60 chains east by north from the winter quarters 

 at Cape Eoyds. (See lower fig. of Plate LXXXVII. p. 266.) It consists of fine 

 gravel and earthy material resulting fi-om the decomposition of keny te. Intermixed 

 with these are numerous remains of serpulfe, with a few foraminifera and echinoid 

 spines. Serpula? were found to be very abundant in the armings of the lead used 

 for sounding at Glacier Tongue in about 157 fathoms. 



The serpulje remains in this patch of raised marine mud were much comminuted, 

 which suggests that the deposit is almost certainly of an upthrust portion of the sea 



