388 Robert L. Jack — On ''Wants*' in Ironstone Seams. 



Devonian — continued. 



4. Xenoneura antiquorum Scudder Devonian New Brunswick, 



5. Gerephemera simplex „ do. do. 



6. Dyscriius vetiistus ,, do. do. 



7. Archimulacris acadicus „ do. do. 

 1. Eugereoti Bceckingii, Dohrn, Permian, Birkenfeld. 



Arachnida 8 



Myriapoda 6 



Coleoptera ... ... 3 



Orthoptera 13 



?? Lepidoptera 1 



Neiu'optera 14 



44 Coal-measures. 



7 Devonian. 

 1 Permian. 



Total Number of Palaeozoic Insects ... 52 



EXPLANATION OF PLATE XL 



F^*^" 2" Und^'^ ^^^^ °^ I Eophrynus {Gurculioid.es) Prestvicii, Buck!., sp., enlarged. 

 From the Ironstone of the Coal-measures, Dudley. Length of specimen 

 14 lines, greatest breadth of abdomen 8 lines. 

 (Drawn from the original specimen in the Cabinet of E. HoUier, Esq., Dudley.) 



II, — On " Wants " in Ironstone Seams ^ and theik Connection 



WITH Faults, 



By Egbert L. Jack, F.G.S., 



of the Geological Survey of Scotland. 



OF all the " troubles" that afflict the Ironstone miner, few are more 

 perplexing than those known as " wants." It sometimes 

 happens that in the course of the working a " face" is being carried 

 forward into the ironstone seam, when the miner finds that he has 

 taken out what is apparently the last piece of " stone," and looks 

 with astonishment at " the blaise where the stone should be." 



The ironstone seam has not thinned out, for it is found that it 

 continues of its normal thickness up to the face, where it abruptly 

 ends. There is no fault or step, for the miner, carrying on his 

 working, finds that in a dozen feet or so the ironstone " takes on 

 attain" as abruptly as it ended off, and may observe that he has had 

 one and the same shale bed all the way for his floor. The roof has 

 simply settled down upon the floor, and the ironstone which should 

 have come between them is not. Such wants are generally found 

 to take the shape of long stripes, inclosed by lines nearly parallel, and 

 about as straight as lines of fault usually are. 



The task before us is to explain why there should be long gaps in 

 strata which without doubt were laid down continuously. The 

 obvious commercial importance of such wants, and the perplexity 

 which seems to prevail regarding their geological origin, lead me to 

 offer the following observations. 



As a matter of fact, wants have hitherto been observed for the most 

 part (and perhaps exclusively) in districts where the strata are much 



1 Only clay-band and black-band Ironstones interstratified with Carboniferous rocks 

 are here referred to. 



