TRANSACTIONS OP THE SECTION'S. ? ( J 



stratigraphieal relations of the beds had been made out, and at present the exact 

 horizons from which many of the species bad been collected was not determined. 



Further, the theory that the Devonian rocks were the equivalents in time to the 

 Old Red Sandstone, required the existence at this period of a great barrier between 

 t lie marine deposits of the former group and the freshwater accumulations of the 

 latter, and there was no physical evidence in support of this. Talcing all the facts 

 into consideration, the author argued that they were in favour of the classifi- 

 cation proposed by Jukes, which regarded the lowermost Devonian rocks as Old 

 lied Sandstone, and the slates and limestones as Lower Carboniferous, formed in an 

 area which constituted a zoological province differing to some extent from that in 

 which these rocks were deposited further north in the British area. 



Notes on the Pcdcpontoloyy of Plymouth. By li. N. Wop.th. 



BIOLOGY. 



Address by J. Gwyn Jeffreys, LL.D., F.R.S., Treus.G.SfL.SS., 

 President of the Section. 



Being merely an amateur naturalist, and not having had any strictly scientific 

 education, I consider it a great honour to be invited to preside over this important 

 Section of the Association. I cannot pretend to give such an Address as may be 

 expected from the President; but I will offer some remarks on a subject in which 

 1 take considerable interest and have done some work, viz. the deep-sea Mollusca. 



The historical part of the subject has been fully treated by Dr. G. C. Wallich in 

 his ' North-Atlantic Sea-bed/ 1862 ; by Professor Prestwich in his Presidential 

 Address to the Geological Society of London in 1871 ; and by Professor Sir Wy ville 

 Thomson in his ' Depths of the Sea,' 1873. 



By the term " deep-sea " I do not mean the zone which the late Professor Edward 

 Forbes called the eighth, and which he supposed to be the lowest and the limit of 

 habitability, in his elaborate and excellent P»,eport on the yEgean Invertebrata, 

 published by the Association in 1844. That zone comprised the depths lying 

 between 105 and 230 fathoms. Nor would I refer to it the " deep-sea " zone which 

 I defined in the Introduction to my work on 'British Conchologv,' 1802; this 

 applied to the British seas only, and extended to the " line of soundings," being 

 about 100 fathoms. Since that time the exploring expeditions in H.M.SS. 

 ' Lightning,' ' Porcupine,' ' Challenger,' and ' Valorous,' as well as in the Norwe- 

 gian frigate ' Yoringen,' have shown that Mollusca inhabit the greatest depths 

 that have been examined, and that life is not less abundant and varied in the 

 abvs3es of the ocean than it is in the shallowest water. Instead of 300 fathoms or 

 1800 feet, which Forbes assumed to be the extreme boundary of submarine life, 

 we must now take 3000 fathoms or 18,000 feet, and even much lower depths. It 

 may be well to distinguish two zones of depth exceeding that which I have termed 

 "the line of soundings;" and I would propose the name "abyssal" for depths 

 between 100 and 1000 fathoms, and " benthal " (from the Homeric word (ievOos, 

 signifying the depths of the sea) for depths of 1000 fathoms and more. 



The first knowledge that I had of the Mollusca from the lowest or "benthal" 

 zone I owe to Dr. Wallich, who kindly gave me a few small shells which he got 

 in a sounding of 1G22 fathoms in N. Lat. 55° 36', W. Long. 54° 33', oflf the coast 

 of Labrador, during his cruise in H.M.S. ' Bulldog ' in 1860. These consisted of 

 undescribed species of Aclis, Homaloyyra, and Pleurotoma, Pteurotoma tenuicostata 



