118 THE LIASSIG PERIODS. CHAP. 



a smaller scale (as to number) the same facts occur in the hills 

 above Cheltenham and in the districts round Stow and Banbury. 



No bed of sand, no sandstone rock, is intercalated in this series 

 of clay deposits; no mark of current occurs in it, beyond such 

 indications as fragments of wood give : it seems the result of quiet 

 continuous or frequently-repeated sediment, brought by the same 

 cause as that which produced the lower lias shale, and was sus- 

 pended during the marlstone period of shallower and more agitated 

 water. 



MIDFOED SANDS, 



The last of the liassic strata, to which the inferior oolite has 

 not quite relinquished its ancient claim, is a variable series of fine 

 sands, deposited on the upper lias clay in such a manner as often 

 to defy the geologist to draw a hard line between them. These 

 sands are bluish underground, yellowish at the surface. They are 

 covered in many districts of the south of England by calcareous 

 and shelly beds, which on the 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. Thus 

 we have in general terms 



Inferior oolite above. 



Shelly calcareous bed. 

 Fine-grained sands. 



Upper lias clay below. 



Here then is a transition series of beds, which for convenience 

 and for reasoning may be joined with either or both of the greater 

 deposits which in fact they feebly tie together. On a fuller study 

 of the case we find as a very general fact (at Blue Wick on the 

 Yorkshire coast, in Lincolnshire and Gloucestershire, and at Lyme 

 Regis) that the passage from the clay below to the sand above is by 

 almost insensible gradation ; while the oolite above seems to connect 

 itself with equal affinity to shelly calcareous rock at its base. 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. 



