HARDWICKE'S SCIENCE-GOSSIP. 



243 



THE GREENSAND AND ITS ORIGIN. 



" * * * but whether it was mechanical abrasion or 

 chemical solution that removed the foraminiferal shells, 

 whose internal casts formed the greensand deposit of the 

 Cretaceous epoch, must remain for the present an open 

 question."— Dr. Carpenter " On the Nature of the Sea-bottom 

 procured by H.M.S. Challenger." (Ann. and Mag. of Nat. 

 Hist., vol. xv., No. S8, April, 18/5.) 



rTlHE author of the paper from which the above 

 -'- is extracted proceeds on an assumption which 

 I have met with repeatedly, and which is based on 

 an oft-quoted statement made by the venerable 

 Ehrenberg in 1853, to the effect that the grains 

 of Greensaud are for the most part, if not 

 entirely, internal casts of Foraminifera in mineral 

 glauconite. Dr. Carpenter has no hesitation in 

 accepting this statement as proved, and, as shown 

 above, with no qualification whatever, nor, as far as 

 appears, with any attempt at verification ; thus 

 giving the weight of his name to the assumption 

 that Greensand is a rock made up of casts of 

 Eoraminifera. Now as it is not a fact that green- 

 sands of the Cretaceous epoch are always composed 

 of foraminiferal casts, it is time that the state- 

 ment of Ehrenberg, indorsed so unreservedly by 

 Carpenter, should be challenged. Living in a 

 district where the Greensand is well developed, I 

 long since unsuccessfully attempted to discover the 

 internal casts of which I was told it was composed. 

 As far as Ireland is concerned this is not so. Eora- 

 minifera to the number of over 100 species abound 

 in the overlying chalk, the specimens being most 

 beautiful and perfect ; but only one species recorded 

 from the Greensand, which, however, is not a cast, 

 but a calcareous shell. This itself is almost con- 

 clusive against the assumption that the glauconite 

 grains are casts, as we can hardly suppose that 

 amongst millions of shells none would escape de- 

 struction. Further, shells of Eoraminifera do occur 

 in the Cambridge Greensand, not mere casts, but 

 perfect calcareous tests, having all the characteristic 

 surface-ornamenation, and without any infilling of 

 glauconite. The occurrence of these shells in the 

 English Greensand does away with the notion that 

 there was something in the waters of the Green- 

 sand seas that was destructive of calcareous shells. 

 Dr. Carpenter also forgets that the Greensand yields 

 us molluscan fossils in abundance, and that not in 

 the condition of casts, but having their calcareous 

 tests preserved, and showing the finest striae un- 

 corroded. I have already stated that I was unable 

 to find any foraminiferal casts in our Greensand, 

 but, as my less-practised eye might err, I requested 

 my friend, Mr. Joseph Wright, F.G.S., to examine 

 the material with the microscope, which he kindly 

 consented to do, portions of the Irish Greensand, and 

 also Greensand from Cambridge, passing under his 

 scrutiny. I have every confidence in Mr. Wright's 

 judgment and acuteness, he having detected in the 



chalk rocks of Antrim, Down, and Derry, in the 

 course of three years over which his examinations 

 have extended, more than 120 species of Foramini- 

 fera and Ostracoda, in addition to sponge spicula 

 and Bryozoa,* being about one-half the number 

 examined by Ehrenberg himself from cretaceous 

 rocks during a long series of years. Mr. Wright 

 was equally unsuccessful as myself; the rounded 

 angular grains are in most cases too large, and pre- 

 sent no real resemblances to the many well-marked 

 forms of Foraminifera. 



The assumption that the Greensand is formed 

 of casts of Foraminifera should be rejected for the 

 following reasons : — 



1st. Foraminiferal shells do occur plentifully and 

 uninjured in the English Greensand ; ergo there is 

 no cause for assuming the wholesale destruction of 

 calcareous shells in that epoch. 



2nd. Calcareous tests of mollusca have remained ; 

 casts are rare in the Greensand. 



3rd, and conclusive. The grains of glauconite in 

 the Irish Greensand, when examined under the 

 microscope, show no real resemblance to Foramini- 

 fera. 



Whilst, for what seem good and sufficient reasons, 

 coming to the conclusion above stated, I do not 

 mean to assert that Ehrenberg stated anything but 

 what was correct as regards the material he ex- 

 amined. Doubtless what he saw seemed to bear 

 out his assertion ; but hasty generalizations are the 

 greatest fault of our times, and it is to be depre- 

 cated that erroneous statements should go forth 

 under the sanction of high authorities in the scien- 

 tific world.' When one finds that Dr. Carpenter 

 makes a false assumption in a matter that comes 

 under our own observation, it is hard to avoid 

 thinking that he may be equally in error regarding 

 such a hazy question as Eozoon versus the mineral 

 ophite. If any reader of Science-Gossip wishes to 

 examine the subject for himself, I will be happy to 

 send him some of our Greensand for that purpose. 



Belfast. S. A. Stewart. 



ABNORMAL FORM OF MALE FLOWER 

 OF VEGETABLE MARROW. 



THE tendency cultivation has to cause a deve- 

 lopment of the sexual organs of plants into 

 floral leaves is well known, but the following case 

 of a plant apparently so little prone to mutation as 

 the Vegetable Marrow may not be without interest. 

 The male flower of this plant consists of a mono- 

 sepalous calyx with five clefts, and contains a 

 single stamen, at the base of which are usually three 

 openings into the nectary, over which the filament 

 forms a sort of vault. 



* Vide "Annual Report and Proceedings of the Belfast 

 Naturalists' Field Club, 1873-74." 



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