1856.] DEGOUSEE AND LAURENT — N. FRENCH COAL-FIELD, 253 



to the west. Many works have, moreover, been undertaken in the 

 course of the last three years in search of a widening of the basin by 

 the series of the seams of caking-coal, and of an extension of the 

 dry-coal-band, which disappears at Choques. With the exception of 

 those made by the " Vendin Company," these sinkings have as yet 

 given only negative results. 



In all the sinkings which have been made from Valenciennes to 

 the furthest of these researches, the Chalk forms the "head" {mort 

 terrain) with a varying thickness. As far as Aire the Chalk alone 

 forms the rock which has to be passed through before reaching the 

 Coal, from which it is separated by a bed of green sand from 1 to 3 

 metres in thickness, known under the name of " tourtia." On the 

 north of Aire it is, in addition, covered up by tertiary deposits, 

 alternations of sands and clays, with a thickness in places of 100 to 

 150 metres, and which render it necessary to line the sinkings as 

 the work advances. This formation is found even in Belgium, at St. 

 Ghislain, near Mons, with a thickness of 60 metres. 



The average thickness of the overlying beds is 140 metres. It 

 seldom exceeds 180 metres, and was found to be only 85 metres at 

 Maries, near Bethune. It is near this town that the depth to the 

 base of the Chalk is the greatest ; the sinkings which have been con- 

 ducted on the south gave a result at a smaller depth. 



Nearly 2,000,000 fr. have been expended by various companies, 

 all formed of private persons, in more than 1 50 sinkings, and nume- 

 rous workings have resulted, which have increased beyond all ex- 

 pression the wealth of these two Departments, have opened up a por- 

 tion of the coal-field of France, and enriched, on a grand scale, the 

 fortunate adventurers. 



The small basin of Fiennes and Hardinghen, near Guines, is inde- 

 pendent of this large one ; it is a coal-deposit in the Mountain 

 Limestone, and has been worked for some time past for local con- 

 sumption ; the coal is found at a slight depth, but the quantity of 

 water renders the workings both difficult and expensive. 



Similar works are progressing in the Dep. of the Moselle, where 

 they are tracing the prolongation of the Sarrebruck basin, beneath 

 the New Red Sandstone. Eight companies have already met with 

 the coal between 200 and 300 metres in depth, and are applying for 

 concessions. It is in this quarter and in the Dep. du Nord that the 

 principal search is now being made, and where we have the greatest 

 number of establishments. 



As to the explorations between Douai and Valenciennes, where 

 only shafts, and perhaps a few sinkings for the study of the ground, 

 have been made, we are unable to give you such information as we 

 have with respect to the new companies, whose recent works present 

 much more interest. 



Herewith we send you a tracing, according to scale, of the works 

 done to the west of Valenciennes, together with an indication of the 

 concessions which have been obtained in the " Departement du Nord " 

 and the '* Pas de Calais," as also the names of the villages where the 

 most important sinkings have been made. (See Plate V.) We have 



VOL. XII. PART I. T 



