1867.] BUETOX PvHiETTC BEDS NEAR GAINSB0E0T7GH. 319 



this comes another bed of black pyritous shale (No. 8), 2 feet 4 inches 

 thick, containing immense numbers of compressed Avicula contorta, 

 Scliizodus cloacinus, and other fossils, and having at wide intervals 

 large, flat-shaped, concretionary nodules, of homogeneous texture 

 throughout, imbedded in its mass. In the more fossiliferous parts 

 this bed is very flaky, and separates easily ; and the flakes, which 

 may be split up into the thinnest slices, seem to be composed of 

 nothing but dead organisms, of which the shells of ScMzodus cloa- 

 cinus form the bulk. 



These last-mentioned shales are capped by a band of very hard, 

 compact, laminated, micaceous sandstone (No. 9), 1 foot 5 inches 

 thick, of a light-grey colour, containing numerous casts of Avicula 

 contorta, Pullastra arenicola, Modiola minima, and Perna, sp., with 

 teeth, bones, coprolites, and drift-wood. This band forms by far 

 the most important of the stone-beds, and has been used largely 

 for the roadways round the new station at Gainsborough. The 

 fossils in it have not uncommonly a bright pyritous covering, ren- 

 dering them very distinct and clear in the surrounding matrix of 

 grey. The markings on this stone-bed are most singular, many of 

 the slabs presenting apparently traces of the moUusks and annelids 

 that crawled over and burrowed in them, with smooth wave-ridges 

 and hollows, the latter filled with shells and fish-remains, just as may 

 now be seen on any sandy shore which the retreating tide has laid 

 bare. This is followed again by a bed of shale (No. 10), 4 inches 

 thick, similar in composition to the other shaly strata, containing 

 Avicula contorta and Schizodus cloacinus in great numbers, above 

 which comes another narrow band of rather dark sandy stone (No. 11 

 in the section), 2 inches thick. Then another bed of fissile shale 

 (No. 12), 1 foot 6 inches thick, containing the same fossils as before ; 

 above which is another band of stone (No. 13), similar to No. 11, 



2 inches thick, and above it shale, as before, 1 foot thick (No. 14). 

 Then comes a remarkable narrow band of highly pyritous stone 

 (No. 15), ^ an inch thick, apparently unfossiliferous ; and succeeding 

 it is another bed of shale (No. 16) 1 foot 6 inches thick, similar to 

 all the preceding. Then a band of stone (No. 17), 2 inches thick, 

 much broken, resembling in this respect the beds of rubble found at 

 the top of Oolite cliffs. This band, which, so far as I have observed, 

 is wanting in fossils, is followed by another bed of shale (No. 18), 



3 feet thick, containing, like No. 8, immense numbers of compressed 

 Avicula contorta and Schizodus cloacinus, with here and there non- 

 continuous veins of black fibrous gypsum running horizontally 

 through the mass, and having near its surface large oval- shaped 

 nodules of septaria, differing from those in No. 8 (which are of solid 

 and homogeneous texture throughout) in being partly hollow, and 

 having their interstices filled with small crystals of carbonate of lime. 

 It is worthy of remark that, where these septaria occur, the black 

 shales directly beneath them dip for a certain distance, and are 

 rounded and compressed by their weight, while the stone-bed 

 above bulges out in a dome-shaped mass, apparently showing that 

 the concretionary action to which these bodies owed their growth 



