Dec. lo, 1885J 



NA TURE 



129 



ijarded as the cause of important or adaptive specific change. 

 Therefore, if it is the case that "so many naturalists accept the 

 theory of natural selection as an exclusive explanation of the 

 evolution of existing species," I think that Mr. Dixon has done 

 well to correct their error. Only I am not aware that any 

 naturalist of note has allowed his belief in Darwinism thus to go 

 beyond the teaching of Darwin. 



George T- Ro.manes 



Scandinavian Ice-Flows 



Failing any more direct answer to Sir J. D. Hooker's query 

 (Nature, vol. xxxiii. p. 79), perhaps, with your usual courtesy, 

 you will allow me space for one or two brief notes. The map 

 referred to, as it stands in " Climate and Time," p. 449, is con- 

 jectural to a very large extent. If we are to take the relative 

 closeness of the lines to indicate comparative depth and strength 

 of the glacier-flow, the Baltic must have been, at the intensest 

 period of glaciation, a glacier-filled valley, on an enormous 

 scale, with the ice-stream passing out over the comparatively 

 low, and then submerged, country of Schleswig-Holstein. Dr. 

 Croll, to support a foregone conclusion, represents it thus, and 

 then makes it bifurcate conjecturally about the Dogger Bank. 

 One or two considerations, however, make Dr. Croll's conclu- 

 sion less " inevitable " than he seems to imagine (p. 449). 



(i) Admitting, as we must, that the striations mentioned 

 (p. 44S) on the Island of Bornholm, point to the passage of ice 

 in massive proportions over at least that island in the direction 

 indicated by the lines on the map, we may still call in question 

 the hypothesis which regards the main mass of the Baltic ice as 

 having passed that way. 



For (2) the evidence given (p. 449) of its having passed over 

 Denmark (the bare " fact that the surface of the country is 

 strewn with debris derived from the Scandinavian peninsula ") 

 is so ambiguous as to be worthless on the point under consider- 

 ation. 



(3) "Xti^ facts stated by Dr. Croll (stripped of the guise with 

 which he has invested them) can be easily and naturally ac- 

 counted for by the action of mtrine ice, owing its origin to the 

 great Scandinavian glaciers of the period ; some of which, even 

 from the Baltic side, probably drifted away into the present 

 North Sea basin. 



But {4) that the main mass of the ice from the eastern slopes 

 of the great glaciated Scandinavian range did not take this 

 direction is proved by some of the best-established facts of 

 European geology ; facts which, had they been known to Dr. 

 Croll, would have rendered, I venture to think, the construction 

 by him of the map referred to impossible. On p. 447 he says, 

 *' After passing down the Baltic, a portion of the ice would 

 probably move south into the flat plains in the north of Ger- 

 many, but the greater portion would keep in the bed of the 

 Baltic, and of course (sic) turn to the right round the south end 

 of Gothland, and then cross over Denmark into the North Sea." 



The naivete of this statement, in a book bearing date 1875, 

 is truly refreshing. Any one who knows the district of Jena is 

 perfectly familiar with the enormous abundance of ice-trans- 

 ported material from Scandinavia to be found thereabouts ; and 

 these "Findlinge" are spread far .and wide over the whole 

 North-German plain as far inland as Bonn, Westphalia, ThUrin- 

 gen. Saxony (even to the south of Zwickau), and, according to 

 Credner's later observations (Sitzber. der imturforsch. Gese'i- 

 schafi, Leipzig, 1875), into the interior of Bohemia, as far as 

 Troppau, near the sources of the Oder, on the slopes of the 

 Sudeten Gebirge, and even to Toula and Moscow. 



(5) Lastly, the occurrence of striated blocks of Scandinavian 

 origin in the boulder-clays of the Yorkshire coast, is clearly in- 

 compatible with the conjectural view so graphically expressed 

 on the map in question. A. Irving 



Wellington College, November 30 



The Resting Position of the Oyster 



I FEEL some disinclination to take up more sp,ace in the 

 pages of Nature on this subject without making any new 

 contribution to the discussion, but Mr. John A. Ryder's letter 

 induces me to summarise the facts which have been brought 

 forward, and the conclusions to be drawn from them. The 

 condition of the oysters examined by me can only be explained 

 by inferring that they were quite free, and resting on a flat 

 bottom with the right valve downwards. The specimens of 



Pecten opcrcularis which I had before me were in^he same con- 

 dition, and doubtless rested in the same position. Of Pecten 

 maximus I cannot speak with certainty, and therefore leave to 

 Mr. Arthur Hunt the responsibility of stating that there is a 

 difference in respect of position in the two species. Prof. 

 Mobius also finds that the left valves of oysters are usually 

 covered by fixed animals, but as far as I understand his letter 

 he thinks this does not prove that the left valves in this 

 condition were uppermost : in the oysters I examined, the right 

 v.alves were so clean that they must have been in close contact 

 with the bottom. The other letters on the subject all describe 

 evidence proving that oyster larvje attach themselves by the lelt 

 valve. This I did not deny, and I might of course easily have 

 found the direct testimony of observers on the subject. Mr. 

 Ryder says it is well known that the right valve of the oyster is 

 always the most deeply pigmented, while the left one is paler ; 

 in the oysters I examined, the condition of the valves was exactly 

 the reverse of this. It seems to me that when a young oyster is 

 attached to the under-surface of a stone or shell by its left valve 

 its right valve is lower, and if it drops from its attachment, or 

 grows much larger than the stone or shell to which it is fixed, 

 the surface of its right valve will come into close contact with 

 the sea-bottom. I h.ive seen oysters which still retained a piece 

 of shell attached near the umbo of the left valve, while the rest 

 of the valve was covered with fixed animals, and the right valve 

 was quite clean and light in colour. There are no crowded 

 oyster-banks in the Firth of Forth, and it might even be said 

 that the oysters which came under my observation had been 

 dredged and thrown overboard again at some time of their lives. 

 But I do not think oysters are often returned to the water when 

 once taken in the Firth. In my former letter I implied that 

 probably in the normal position of an adult oyster the right 

 valve was in contact with the bottom. That this is often the 

 case when the oyster is free and has plenty of room has not yet 

 been disproved, and therefore I think the current statement that 

 the oyster, when not attached, invariably rests with its left valve 

 downwards needs modification. J. T. Cunningham 



Scottish Marine Station, November 28 



The Sea-Mills at Argostoli 

 I WILL be glad if, through .the columns of your journal, you 

 will be good enough to inform me what has been written in 

 English concerning the phenomenon known as "The Sea-Mills 

 at Argostoli." Having recently visited the island of Cephalonia 

 I was able to examine these mills frequently, and I have 

 reasons for believing that papers have been read at diflferent 

 times at some of the learned societies at home discussing the 

 subject ill extenso. I will therefore be glad of any intelligence 

 on this interesting phenomenon which you may be able to refer 

 me to. J. Lloyd Thomas 



H.M.S. Temc'raire, Mediterranean, November 15 



Earthquake 



On Thursday morning, December 3, I was in bed awake, 

 between 6 and 7 o'clock. I heai-d a slight clattering noise 

 of the earthenware and glass articles on the marble top of 

 the washstand. It lasted for about three seconds, and went 



with a slight halt near the end. There was no one 



moving in the house, and nothing outside to cause the tremors, 

 which I did not feel in bed. I immediately got up to look at 

 the clock, and found it was 6.45. I do not know at what time 

 the earthquake in Algeria took place, possibly there was some 

 connection between the two, and the tremor may have been felt 

 in other places in England, so I record this. 



Gateshead, December 6 R. S. NEVifALL 



VENTILATION 

 T N modern life, with its enormous populations living 

 ^ under artificial conditions in towns and cities, the 

 subject of ventilation, or the supply of sufficient pure air 

 to each individual for the maintenance of health, has 

 assumed, as it has become more generally understood, a 

 vast and national importance. Its importance has been 

 clearly demonstrated in many instances by a greatly 

 diminished death-rate in places where overcrowding on 

 space or in houses, formerly e.xistent, has been remedied, 



