142 Corres-poiidence—L. F. Sj)at}i. 



Such characters as size, specific gravity, chemical stabihty, and 

 solubility all influence transportation and subsequent preservation 

 of the mineral grains which go to form sediments. The manner of 

 disintegration of the parent rock is of importance in determining 

 the initial size of grains derived from it. The agent of transport, 

 whether wind or water, takes charge of the loose grains, and sorts 

 or mixes, preserves or destroys, according to its particular attributes 

 of speed, temperature, and composition. Solution after deposition 

 may sooner or later remove the far-travelled remnant. These and 

 other principles were passed in review. Finally, a most interesting 

 discovery was announced. All the way from Sutherlandshire and 

 the Orkney Isles, in the north, to Yorkshire, in the south, sand- 

 stones and grits, ranging in age from Pre-Cambrian to Triassic, are 

 apt to yield deep purple-coloured zircon in beautifully rounded 

 grains ; and this zircon has almost certainly been derived from 

 some area lying outside of Britain. 



THE AMMONITE SIPHUNCLE. 



Sir, — In his interesting paper on the " Ammonite Siphuncle " 

 in last month's Geological Magazine, Dr. A. E. Trueman rejects 

 my suggestion (adapted after Pictet, etc.) that a (not the) function 

 of the siphuncle in Nautilus was to afiord a means of attachment 

 of the animal to its shell. I would gladly welcome a theory that 

 explains all the facts (which my suggestion does not do), but, un- 

 fortunately. Dr. Trueman does not offer a better explanation. He 

 considers as more reasonable, however, the opinion of Drs. Foord 

 and Woodward, who had suggested that the sij^huncle was " of 

 more importance in the young, perhaps then serving for attach 

 ment . . ." Thus, it may be attachment after all, and the objections 

 that I would adduce against my own explanation. Dr. Trueman does 

 not mention, namely, (1) that histologically the siphuncle oi Nautilus 

 is not a ligament, and (2) that the concentric muscle-lines indicate 

 a gradual shifting of the shell-muscles during growth, concurrently 

 with the secretion of gas. But, while perfectly willing to admit 

 that in some j)rimitive Nautiloids and also in the young of 

 Ammonoidea (which then had simple se|)ta) the evidence of attach- 

 ment is, perhaps, stronger, I do not think that we are justified 

 in assuming, as Dr. Woodward did, that the function of the siphuncle 

 is performed, in the adult Nautilus, by the shell-muscles, as though 

 these structures Avere not present in the young. Nor is there 

 any evidence that the siphuncle is of less functional importance 

 in the recent Nautilus than in a homoeomorj)hous Silurian shell, 

 or again in a Cretaceous Ammonite than in a Devonian Goniatite. 



My contention was that during a forward move of the shell- 

 muscles (the peculiarly pitted appearance of the scars in some 



