AUSTEN — EXTENSION OF THE COAL-MEASURES. 



41 



effected, and the White Chalk and certain subjacent beds, altogether 

 about 800 feet, were found superposed on palaeozoic sandstone and 

 shale. 



At Calais, which is about 18 miles to the north of the old coal- 

 works at Ferques, an artesian well was carried through the thickness 

 of the Chalk, and at a depth of 1 100 feet beds were met with which 

 have been identified as true coal-measures*. By the aid of the fore- 

 going data, it becomes easy to carry on the section of the palaeozoic 

 series, as exhibited in the Boulonnaisf . 



s. 



N. 



Oolitic series. 



-Cretaceous series.- 



# 





•5' -^ ,^ 



«i. 



t 



C* ^ "^ ^ 



'^ ^ "t- °. 





^^ 



B-^ ^ ^ ^ ^ ^ ■§ ^ S ^ ^ 



§ -^ ^ -^ 



2. .S. 4. 5. 1. 2. 3. 4. 5. 6. ^ 



<u 



t* ^ ^ r* ^ 



'S. ^ 'Ji 'i 



O ^ O ^ O '^ 



w, tP, ■§! '^ ;*. ?- ';4 



^ ^ ^ ^' 

 ^ '^ ^ X* 



(S * 



-Garb, series. Upper Eifelian. 



Middle Eifelian. 



?. 7- 6. 



Upper Eifelian. Garb. Series. 



By this it will be seen that on the north the cretaceous strata im- 

 mediately overlie a higher portion of the palaeozoic series than the 

 oolites do in the south, thus giving considerable extension to the area 

 over which that series is wanting. 



The circumstance, that a portion of the coal-measures should have 

 been recognized so near us as at Calais, has suggested the following 

 inquiries, which relate, — 



1 . To the amount of h 'priori evidence as to whether the coal-series 

 may be continued further West, across the Straits of Dover, and so 

 beneath our south-eastern counties. 



2. Whether, if so, the coal-measures are likely to occur under such 

 condition of depth, with respect to the overlying formations, as would 

 render them available to us. 



The solution of such questions depends on a great variety of con- 

 siderations ; and more than ordinary caution is imposed on any one 

 who would venture on an affirmative opinion. "Le probleme qui, sou- 

 levent les recherches de mines de houille dans le nord de la France, 

 se rattache en derniere analyse au plus grandes questions que la 

 geologic puisse traiter relativement aux couches houilliers de ces 

 contrees ; celle de la forme, encore indeterminee, du bassin dans 

 lequel elles se sont deposes, celles de la disposition des terrains qui 

 ont reconvert le terrain houilher dans une grande partie de son 

 etendue." 



* Prestwich, Geological Inquiry respecting Water-bearing Strata, &c., p. 208. 

 t Quart. Joum. Geol. Sec. I.e. 



