1846.] MURCHISON ON THE GEOLOGY OF GOTHLAND. 23 



In these strata, particularly in the sandy limestone and oolite, we 

 speedily procured numerous specimens of the shell figured by Hi- 

 singer as the- Avicula retroflexa, and repeated by me in the 'Silurian 

 System.' It was the occurrence of this fossil which formerly led me 

 to suppose that the southern end of Gothland would be found to 

 differ from the mass of the island, and would eventually be placed 

 in the parallel of the Ludlow rock, in which that striking shell 

 occurs in England. When we fairly determined on the spot, that 

 this species of Avicula was undistinguishable from that of Britain, 

 and further saw that it was here, as in England, associated with 

 the spinose Leptcena lata or Chonetes sarcinulata, a fossil nevei 

 found in any inferior Silurian strata, whether in Northern Gothlanci 

 or in England, and also that these shells were mixed with othei 

 forms of Avicula, Cypricardia and Turritella equally unknown ir. 

 the northern limestones of Gothland, but strikingly representing the 

 collocation of shells of the Upper Ludlow of England, there was no 

 longer any doubt that we had pursued an ascending section from 

 the north, and were now fairly amid the equivalents of the Ludlow 

 rocks of England. Among the other Ludlow rock fossils, Mr. 

 Sowerby has since my return to England identified the Terebratula 

 pulchra, Cypricardia retusa, Pleurotomaria articulata and Turbo 

 corallii of Grotlingbo with species of the Upper Ludlow rock. We 

 here also found fragments of Trilobites and a small Battus or Agnos- 

 tus, identical with the A. tuberculatus published in the ' Silurian 

 System' from the Downton Castle building-stone of the Ludlow 

 rock*. 



In this district we soon indeed obtained positive proof, that the 

 beds dip to the south, though the inclination is so slight that no in- 

 dication of it can be detected in a single locality. 

 ,,; The quarries of Grotlingbo, where the peculiar shelly oolite and 

 jsandstone occur, are, as before said, about seventy feet above the 

 sea ; but on descending from them and passing southwards for four 

 English miles along the marine bay called Bursvik, the same beds 

 of calc grit, oolite, pisolite and sandstone (containing the very same 

 shells) are next detected, close to the little port of Bursvik, at a 

 height of not more than twenty feet above the sea ; whilst near the 

 promontory of Hoburg, a few miles further south, they are actually 

 on a level with the water. The diagram (fig. 11) explains therefore, 

 by stratigraphical evidence, that the Upper Silurian oolite and sand- 

 stone (i) dip away from the great masses of limestone and shale (e^f, 

 g^h), of which the central and northern portions of the island are 

 composed, and distinctly pass under the limestone of Hoburg (k). 



These quarries at Bursvik and Mount Hoburg have been long 

 opened, and they are the only valuable sources in the island for the 

 extraction of free-stone, which is available for building and roofing 

 purposes and for whetstones. This fine and slightly calcareous 

 psammite is as greedy of water as portions of the Ludlow rock, 

 like which it increases astonishingly in weight upon exposure to 



- * This crustacean, I would here observe, is distinct from the yi,pisiformis of the 

 Lower Silurian rocks. 



