46 TYPE AMMONITES— IV Aug. 



The following Sequence (XIX) of Scottish rocks is taken, with 

 abridgements, from the first of the masterly papers by J. W. Judd 

 on the Secondary Rocks of Scotland (Q.J.G.S., XXXI, 1873, 97-195). 

 The sequence is that of his Tab. II ; but for the correlation with the 

 Sequence already given (Seq. IX, p. 40) the fuller details of his Tab. I 

 have been utilized. Sequence XIX is not given for any evidence of 

 faunal succession, but for its value as presenting a bird's-eye view of 

 the nature and thicknesses of the strata — necessary data for palaeo- 

 geographical reconstruction, to combine with the evidence of Ammonites 

 in any such essays. 



Sequence XIX — ^Scotland, East Coast 



(J. W. Judd, 1873, Tables I, II, abbreviated) 



Correlation Strata Nature Thickness 



(T.A. IV, p. 40) (in feet) 



? z. Light-coloured and ferruginous sandstones Estuarine 100 + 



Coarse shelly "^ f Marine ^ 



-ry r, J limestones 1 Brecciated J Marine I 



' *^ ^ Carbonaceous ( Beds j & f 



shales J (^ Estuar.J 



Sandstones (casts of marine shells) Marine so.-* 



Sandstones, coaly seams Estuarine 150 + 



Sandstones, marine shells Marine ? 



Limestones, clays and sandstones Marine etc. 200? 

 Sandstones, coaly seams 



(several marine bands) Estuarine 400 



Fine-grained sandstones Marine 25 



Sandy shales, few fossils Marine 150 



Pyritous and laminated shales Marine 80 

 Black laminated shales, 



septaria, shelly bands Marine 70 



IX, 29 n. Calcareous sandstone (" Roof Bed ") Marine 5 



In this Sequence there are more than 1730 feet of strata. Allowing 

 for beds not measured, there may be supposed to be over 2,000 feet from 

 Callovian to lower Kimmeridgian (Proplanulitan to Physodoceratan), 

 and yet there are several gaps. 



This brings to a close, at any rate for the present, the account of 

 the Chronology of the Jurassic so far as the Upper Oolites are concerned. 

 It will be for the next volume to carry the study further. But the present 

 opportunity may be taken to say a few words upon the method used 

 in constructing the Hemeral Tables from the evidence of the Sequences, 



A good example is furnished by a comparison of the Portland beds 

 of Oxfordshire (Seq. II, p. 28) with those of Swindon (Seq. Ill, p. 29). 

 In the iirst case, one stratum, Shotover Grit Sands, gives three elements 

 in the fauna without evidence as to their sviCce.s?,\on— Par avirgatites, 

 Am. cf. devillei and Am. pectinatus : a definitely lower bed, the Wheatley 

 Sands, of different lithic character, yields another element, Wheatleyites. 

 So far, there is evidence for no more than two hemerae. Let these be 

 called, provisionally, pectinatus and Wheatleyites. But Swindon shows 

 no change of matrix during these two hemerae — that is to say, the species 



