AUSTEN EXTENSION OP THE COAL-MEASURES. 59 



Combining these features and conditions with those presented by 

 our own Northern, Midland, and Southern Coal-measure series, we 

 arrive at the relative positions of areas of land in various quarters, 

 and which, if taken in conjunction with the extent which has been 

 assigned to the Scandinavian range, define the boundaries of an 

 internal sea, around and occasionally over large parts of which 

 the peculiar vegetation of the time was developed and entombed as 

 the area rose and sank. A region with a central depressed area, 

 such as Australia is supposed to present, and going down, by means 

 of a long series of oscillations, would ultimately present just such 

 an assemblage of deposits as our own Carboniferous group. 



B. Axis of Artois. 



In the physical topography of the old County of xlrtois there is a 

 linear ridge, which, commencing at the S.E. extremity of the Bou- 

 lonnais denudation, extends in a direction S. of Arras (W. 34° N.) : 

 its highest points are a little S. of Desire, the hill north of Senlecques, 

 and near the windmill on the road from Boulogne to St. Omer, about 

 two miles beyond the village of Escouilles, which reach nearly 700 

 feet : thence the line may be drawn by Bellevue, 616 feet, Coupelle 

 Neuve, Crepy, Fiefs, 609 feet. Sains, Tangry, Valhum, Aulin, Orlen- 

 court, 550 feet, to the E. of Tinques, and then S. by Penin to Grand 

 Rullecourt, 543 feet, the altitudes decreasing from N.W. to S.E. ; 

 nor does it cease near Arras, but trends away with a rather more 

 southerly direction towards St. Quentin. On one side, the Lys, the 

 Scarpe, the Scheldt, and other streams take their rise and flow into 

 the North Sea. On the other, the Canche, the Authie, and the 

 Somme discharge into the English Channel. It will also be seen 

 by reference to the map that the physical structure of the whole 

 district as far as the Valley of the Seine is in strict parallelism with 

 the line of Artois. 



In 1845, M. d'Archiac, in a memoir already referred to, pointed 

 out the influence which a line, coinciding with that of the axis of 

 Artois, had had on the character and limits of the Middle and Lower 

 Cretaceous deposits. The most remarkable point connected with this 

 axis was noticed by Monnet as far back as 1780*, who showed that 

 along a line which lies a little to the north of the watershed the 

 Chalk had been fissured, so that traces of the old world (Palaeozoic 

 strata) were to be seen in apposition with the new, as the Chalk was 

 then considered. 



If any relation can be traced between the lines of disturbances and 

 fractures presented by the uppermost strata along the axis of Artois 

 with those which have happened along the same line at times long 

 antecedent to the formation of such overlying strata, and if this 

 repetition can be referred to a necessary law, then the surface-struc- 

 ture throughout such lines becomes a serviceable indication of that of 



* Description Mineralogique de la France, Atlas, pi. 3. 



