140 THE LIAS AMMONITES. 



Gloucester, Somerset, Dorset, and York, the Cephalopoda-bed and its underlying 

 sands were shown to represent a well-marked horizon with specific forms of Ammonoida 

 that were found neither in the Alum-shale or Bifrons-h&dL below, nor in the Inferior Oolite 

 or Murchisonm-ifyas, above, and certainly represented a horizon of life, the correlative of 

 the Jurensis-Mergel of Quenstedt. 



The late Professor John Philhps^ proposed the name " Midford Sands " for " the last of 

 theLiassic strata to which the Inferior Oolite had not quite relinquished its ancient claim. 

 .... They are covered in many districts of the south of England by calcareous and 

 shelly beds, which on first view appear naturally associated with the Oolitic rocks above ; 

 but they contain many fossils which are frequent in the Sands and not common in the 



Oolites If we wish to draw a hard limit of mineral deposits it should probably 



be between the sand and its calcareous cover (which is often absent), but if we desire to 

 study organic sequence we shall unite the sands and their shelly cap into a transition 

 group. In this point of view the facts which have come out by inquiry are very 

 instructive. Taking first the group Cephalopoda, we find some of the well-known 

 species of the Upper Lias to be continued through the sands into the shelly bed above, 

 as Ammonites bifrons, A. opalinus, A. striatuhis, A. coneavus, Belemnitss compressus, 

 B. irregularis, B. tripartitus. On the other hand several Conchiferous Molluscs, which 

 occur with these Cephalopoda, have decided Oolitic and not Liassic affinity. Such are 

 Hinnites abjectus, Trigonia striata, Modiol'a Sowerbii, Pkoladbmya fidicula. Before the 

 Liassic life has come to an end the Oolitic life has begun ; a point of great importance 

 in the reasoning on the causes of successive variation in the oceanic population, and one 

 which will come before us again on several occasions while following the course of Oohtic 

 time. The Cephalopoda-bed . . . . is not known in the valleys> of the- Gherwell or 

 Evenlode, and very partially in any of the branches of the Windrush, Coin, or Churn. 

 But on the western front of the Cotteswold cfiffs it extends from Cleeve-Cloud to 

 Wotton-under-Edge, appears on the Dorsetshire coast, near Bridport, and is recognised 

 in France." 



In the palseontological table which accompanies this section it will be shown that 

 Harp, striatulum and Harp, ofalinum are not found in the Upper Lias properly so called, 

 but appertain to the Jurense-\>%A, and that Harp, bifrons is a leading fossil of the clay 

 bed of the Upper Lias, but is not found in the Jurense-ione unless as a fossil washed out 

 of an older bed and redeposited in a newer formation. 



Dundry Hill, near Bristol, 769 feet in altitude above sea-level, is the most westerly 

 outlier of the Cotteswold range, from which it is nine miles distant ; this is a locality of 

 great interest to the naturalist, as it affords capital sections of the Jurassic strata, 

 admirable examples of rock-sculpture by denudation, and a commanding point for 

 surveying the grand panorama in the midst of which it stands. The following profiles 

 of this hill show its structure very clearly. 



* ' Geology of Oxford and the Valley of the Thames,' p. 1 18, 1871. 



