1859. J HULL THINNING-OUT OF THE SECONDARY BOCKS. 69 



traced for a distance of two miles, with an average dip of 15° to the 

 S.E. From this section alone a thickness of 2300 feet may be 

 estimated ; and, judging from the interval between the point where 

 the section ceases and the Lias boundary at "Whitchurch, the 

 thickness must be much greater. From various comparisons it 

 appears probable that from 3000 to 3500 feet is not an over- 

 estimate. Now, in Staffordshire, Leicestershire, and the central 

 districts generally, the Eed Marl does not exceed a thickness of 

 600 or 700 feet, showing a great decrease towards the S.E. from 

 Cheshire (Plate IV. figs. 2, 3). 



The direction of maccimum attenuation, however, is along a line 

 drawn S.E. from the Estuary of the Dee, and passing near Nant- 

 wich, Stafford, and "Warwick, beyond which the formation is lost 

 below the Lias. If we put down as the thickness at each of these 

 places respectively, 3000, 700, and 400 feet, we shall have probably 

 a just conception of the rapid thinning-out of these beds ; and 

 it therefore appears by no means improbable that even this great 

 argillaceous series is extremely thin, or altogether absent, in Oxford- 

 shire and Northamptonshire. 



If, then, we compare the section of the Trias, as it occurs in 

 Cheshire and East Warwick, we find the following result: — 



feet. 



f Red Marl 3000 



Cheshire -j Lower Keuper Sandstone 450 



[ Bunter Sandstone 2150 



Total 5600 



f Bed Marl 400 



East Warwickshire < Lower Keuper Sandstone 200 



[ Bunter Sandstone absent 



Total . 600 



In other words, the formation is ten times thicker in the former 

 than in the latter county. 



2. Claim of the Trias to Consideration. — A formation which attains 

 so great a development deserves, I think, a larger share of attention 

 than it has yet received from geologists. There are few groups which. 

 in the almost entire absence of fossils, have so strongly stamped upon 

 them the impressions of varying physical changes during their 

 growth. We find in it stages which have been strongly influenced 

 by current-action, and others of apparent tranquillity. We thul 

 shingle-beaches, some traceable to their coast-lines, and conglo- 

 merates which have been drifted from regions comparatively remote. 



Its structure, however, presents phenomena of much interesl to 

 the physical geologist. It is frequently traversed by systems of 

 faults, which, in the form of escarpments, ridges, and valleys, have 



left their marks in the configuration of the surface* ; and no person 

 * In mam districts <<{ Cheshire, Salop, sod Staffordshire, tin- oo-ordinate lines 



of fracture, with their cross-fractures, limy lv very readily traced bj the features 



