244 Notes and Comments. 



not isochronous, but are separated by a time-interval which 

 corresponds to a thickness of some 300 feet of deposit in the 

 Scottish area. Thus, instead of the simple descending sequence 



Deroceras artnatum 

 Echioceras raricostatum, 



there is this sequence ascertained : 



An upper Deroceras horizon, 



An upper Echioceras horizon in three distinct stages, 



A lower Deroceras horizon. 



A lower Echioceras horizon with some Armatoids ; 



and even now possibly this is not the end of the complication. 



AMMONITE NOMENCLATURE. 



In the discussion which followed, Mr. G. W. Lamplugh, 

 F.R.S., said that, while recognizing the scientific value of this 

 intensive study of the Liassic ammonites, he feared that the 

 Author's continued refinements of the nomenclature and 

 zonal classification had carried the subject beyond the reach 

 of the ordinary field-geologist. From the imperfect nature 

 of the evidence, such exactitudes as those shown in the tables 



* could rarely be applicable in the field. The use of fossils by 

 the stratigrapher in the past, though crude, had generally 

 been effective for his purpose ; but he could not be expected 

 to master the complicated technicalities of these new methods. 

 The stratigraphical deductions drawn solely from these palae- 

 ontological studies did not inspire confidence. 



SECONDARY RUTILE IN MILLSTONE GRIT. 



Mr. H. W. Greenwood recently read a paper to the Liver- 



• pool Geological Society, ' On an interesting Occurrence of 

 Secondary Rutile in the Millstone Grit.' The grit in which 

 the rutile occurs forms the base of a long ridge of hill which 

 commences about a mile north-east of Macclesfield, runs for 

 about two miles in a northerly direction, and terminates just 

 above the village of Bollington. The particular exposure 

 described occurs in a quarry on the hillside overlooking 

 Bollington. The rock contains a quantity of light yellowish 

 interstitial decomposition product, and it is in this and also in 

 small cavities lined with iron-stained debris that the secondary 

 rutile occurs in little glistening grains of a brilliant pink colour, 

 sometimes deepening to a port wine tint. In some parts of 

 the rock the crystals occur in such quantity as to become the 

 dominant heavy mineral. The evidence points to the rutile 

 having been formed from the alteration of a titaniferous biotite. 

 In addition to the secondary rutile there are also deep yellowish 

 red usually rounded grains which form part of the original 

 constituents of the rock. Anatase is also abundant, generally 

 growing on leucoxene, and staurolite was also noted. 



Naturalist, 



