350 MR. J. W. GREGORY ON THE 



the specimen to remain for some time in England, and thus several 

 specialists, includinp; Profs. Moebius and Nicholson, have been 

 enabled to examine it. 



Considering, therefore, the importance that has been attached to 

 this specimen throughout the whole controversy, it has been thought 

 that a redescription may be of value. The note upon it is sent to 

 this Society, as the ])iates illustrating the specimen were first 

 published in its Journal. 



(a) General Form. — As reference to the original figure* will show, 

 the specimen consists of a series of narrow white bands of calcite 

 separated, though often imperfectly, by bands of a darker-coloured 

 limestone, which are often continuous with the matrix on eitlier 

 side. The former, which are neither as numerous or regular in the 

 specimen as in the figure given in the Journal, are wider at one end 

 than the other, and thus mark off a somewhat clavate-shaped area 

 of the slab. The view taken by Sir J. W. Dawson is that the white 

 bands of calcite form the original " intermediate skeleton " of an 

 Eozoon colony, while the darker layers between them represent the 

 " body-cavities " filled up by the material that forms the mass of 

 the limestone. 



(b) The Microscopic Structure of the Roch. — The rock itself is a 

 calc-mica-schist in which the remains of the bedding-i^lanes are 

 recognizable though obscuref. When examined under the microscope 

 the cleavage is seen to be due to the development of crystals of a 

 white mica, while the dark colour arises from minute particles 

 of graphite scattered irregularly throughout. A few small quartz- 

 fragments, which may represent original sand-grains and patches of 

 a grey calcareous mineral (probably dolomite), are also to be noted. 

 Mr. Teall has verj' kindly examined the slide ; he observes that it 

 reminds him much of some of the Assynt limestone which has been 

 altered by contact with granite, and, as he accepts the micas as 

 authigenous, there can be no doubt that the rock is a true schist. 

 The abundance of graphite gives it a resemblance to the grey 

 " cipolinos " of the St. Gothard, but it is less altered than these. 



(c) The '^ Eozoonal Bands." — The ''^Eozoon" is preserved on the 

 surface of a slab of the calc-mica-schist, and an examination with 

 the naked eye shows that three sets of structure traverse the rock. 

 The cleavage is parallel to the face of the slab, and this it was that 

 Sir J. W. Dawson regarded as " the plane of stratification," a view 

 which an examination of a transverse section clearly shows to be 

 untenable. The true bedding-planes cross those of cleavage at a 

 fairly high angle and run parallel to the obliquely -truncated upper 

 margin ; their traces on the sides are intensely crumpled and con- 

 torted. They can be clearly seen on the upper surface, but are not 

 shown in the original figure. They are, however, well marked in a 



* Quart. Joiirn. Geol. Soc. vol. xxiii. (1867) pi. xi. ; reprinted in Amer. Joiirn. 

 Sci. 9or. 2, vol. xlvi. (1808) pi. i. ; Dawson, 'The Dawn of Life' (1875). pp. Ill, &c. 



t The rock is a limestone, as Sir J. W. Dawson has stated ; but on close 

 examination it is seen to belong to the schistose-micaceous variety termed by 

 petrologists a calc-mica-schist. 



