HAIiDWICKE'S SCIENCE-GOSSIP. 



31 



origiu. That this has not been determined by pre- 

 vious observers is partly due to the use of acid, 

 after Ehrenberg' s directions, in preparing the sand; 

 this of course would obliterate the calcareous lines 

 which distinguish the lobations. The silica and 

 various silicates mingled with the glauconite grains 

 must have thrown the analysis of these grains 

 hopelessly wrong." 



Taking now Mr. Stewart's second objection, that 

 the calcareous tests of mollusca have remained, and 

 that casts are rare in the greensand,— according to 

 the context this should refer to the English green- 

 sand, and such a statement sounds somewhat 

 strange to any one acquainted with the fauna of the 

 Cambridge bed, the greater part of which, or some 

 two hundred species, are only found in the state of 

 phosphatic casts; it is true I regard these as 

 derived by erosion from the gault ; the fact never- 

 theless remains that they are now in the greensand 

 or chloritic marl, which here forms the basement 

 bed ot the chalk. 



Again, take the chloritic marl of the Isle of 

 Wight. Here casts are CDtnmon, some fossils, such 

 as the Ammonites, rarely retaining their calcareous 

 tests, while those shells that do remain, such as 

 those of the Lamellibranck Molluscs, have always 

 lost their internal nacreous layer, so that any traces 

 of the hinge or internal muscular impressions are 

 rarely visible. This is indeed the ordinary state of 

 shells in many glauconitic and all chalk strata, and 

 I x-egard it as a very significant fact, which may 

 possibly find its explanation in that very presence 

 of carbonic acid in excess at great depths, which 

 Dr. Carpenter and others have suggested to account 

 for the removal of the foraminiferal shells on the 

 sea-bottom. 



The third reason (which Mr. Stewart regards as 

 conclusive !) simply amounts to the fact that the 

 Irish glauconite grains, though carefully examined 

 by himself and Mr. Wright, show no resemblance 

 to Foraminifera. This may be so, and it is of course 

 worth ascertaining; possibly, however, acid has 

 been used in these examinations, which, as Mr. 

 Sollas has pointed out, increases the difficulty of 

 recognizing their true origin. And even suppos- 

 ing that these Irish greensands are not composed 

 of foraminiferal casts, I fail to see how that is a 

 conclusive objection to their forming the main con- 

 stituent of other greensands. 



It is not necessary for Dr. Carpenter's argument 

 that all greensands should be so constituted ; it i 

 sufficient for him that such should frequently be the 

 case ; and of this there can, I think, be little doubt, 

 if Mr. Stewart will accept the statements of other 

 authorities in the scientific world. 



Besides the testimony of Professor Ehrenberg and 

 Mr. Sollas regarding greensands, Professor Bailey, of 

 the United States, was the first to ascertain that 

 the process was going on at the present time in 



the Gulf of Mexico. Dr. Carpenter has also obtained 

 such casts both from dredgings in the iEgean and 

 from Mr. Jukes's Australian dredgings (see a paper 

 in Proc. Roy. Soc, 1875, p. 2-12). Lastly, I may 

 quote from a paper read before the Geological 

 Association last year (p. 2i) : "The observations 

 recently made in the ' Challenger ' show that all 

 along the line of the Agulhas current there is a 

 greensand covering the bottom. Now, as Pro- 

 fessor W. Thomson says, we should simply have 

 noted this as greensand if we had not had in our 

 mind the observations of Professor Ehrenberg. 

 Looking at this greensand with a microscope, we 

 are able at once to recognize the grains as. almost 

 entirely the internal casts of Foraminifera." 



With regard to the question raised by Dr. Car- 

 penter as to whether the absence of the shells is 

 attributable to mechanical abrasion or chemical 

 solution, I am inclined to think that sometimes one 

 cause, sometimes the other, has been in operation. 

 In the Cambridge greensand it is, 1 think, chiefly 

 due to abrasion, the co-existence of shells and casts 

 in that bed being thus accounted for. Supposing 

 them both to have been contemporaneous with its 

 deposition, it is difficult to see why some should be 

 in the state of casts, and others retain their shells in 

 aperfect and uninjured state ; but on the hypothesis 

 that the latter only belong, so to speak, to the indi- 

 genous fauna, while the former have been derived 

 from the Upper Gault, their association in so thin a 

 bed receives a perfectly natural explanation. 



It would, perhaps, have been more prudent 

 in Mr. fctewart to have asked for informa- 

 tion on the subject, rather than to have given an 

 unqualified denial to observations which are made 

 by competent men, and he is especially unfortunate 

 in remarking that "hasty generalizations are the 

 greatest fault of our times, and it is to be deprecated 

 that erroneous statements should go forth under the 

 sanction of high authorities in the scientific world." 

 1 most cordially agree with this sentiment, and the 

 present communication has sprung from a similar 

 wish, viz., that erroneous statements and hasty 

 generalizations should not be put forward by any 

 one professing to be a scientific man. 



Cambridge. A. J. Jukes Bkowne. 



" It has often been vaguely asserted that plants 

 are distinguished from animals by not having the 

 same power of movement. It should rather be said 

 that plants acquire and display this power only when 

 it is of seme advantage to them ; this being of com- 

 paratively rare occurrence, as they are affixed to the 

 ground, and food is brought to them by the air and 

 rain. We see how high in the scale of organization 

 a plant may rise, when we look at one of the more 

 perfect tendril-bearers."— Darwin on the "Move- 

 merit and Habit of Climbing Plants." 



