8 o. LINDSTRÖM, ON TIIE SILURIAN GASTROPODA AND PTEKOPODA OF GOTLAND. 



Fossils have been found in the shale <ind sandstone beds, which long had been regar- 

 ded as distinguishing the Upper Ludlow rocks. Such are Phacops Downingiai, Homa- 

 lonotus etc. But this must not detain us any longer, as also in England, according to 

 the last editions of Siluria., the Ludlow beds have very few species, which are not also 

 found in older strata. Homalonotus and Chonetes striatella, once supposed to be so cha- 

 racteristic and exclusive, are now also found in the lowest Wenlock beds, both in England 

 and Gotland. It cannot, however, be denied, that there are rnany circumscribed fau- 

 nistic areas, as for instance in the shale along the west coast from Westergarn to 

 Petesvik, including Stora Carlsö. Within this region there can be discerned at least 

 four different facies in the distribution of the fossils, of which I have given detailed 

 lists in the paper above cited^). Although there cannot be the slightest doubt that the 

 shale beds of all these localities, as stated, lie on the same level and are coeval, the 

 stränge fact is obvious that the beds of Stora Carlsö have a fauna identical with the 

 shale of Westergarn, which is a Swedish mile and a half distant. The fauna of Eksta 

 at Djupvik is distinct with regard to its composition as well as its features in the 

 comnion species, from both Westergarn and Petesvik in Habblingbo, but farther inland, 

 at Fardhem, species from both Habblingbo and Eksta meet in the same bed. So again 

 the fauna of Westergarn is distinct from that of Wisby, though both have species in 

 common not raet with anywhere else, as Leperditia Hisingeri, Lindströmia Dalraani, 

 Oriostoma Roemeri and others. But, upon the whole, stränge as such dififerences in 

 nearly situated localities may seem, when they cannot be accounted for through 

 changes due to time, they may, nevertheless, find their counterparts in other strata, as 

 well as in the sea as it now is, where differences in depth or in the mineralogical nature 

 of the bottom, cause contiguous regions of the littoral belt to differ in their faunas. 



Stratum b. In northern and central Gotland a stratum of thin limestone flags 

 interstratified with seams of coarse marly shale succeeds the stratum a. It attains a 

 thickness of 70 feet, though at many points much less. Above the sandstone in the 

 south of Gotland this rock is changed into coarse pisolite or oolite with a thickness at 

 the highest of 20 feet. The change from limestone to oolite can be traced almost as 

 gradually as that from shale to sandstone. The banded limestone reappears above the 

 oolite in the section of Hoburg. 



The stratum c, commonly called crinoidal- limestone, covers almost the whole 

 of the northern and central part of Gotland and, being denuded away över a large 

 tract, between Burs and Sundre, it forras again the numerous hills around Hoburg. 

 Its thickness amounts to at least 150 feet, measured from the steep cliffs of Lilla 

 Carlsö, but owing to denudation it is seldom so considerable. The total amount of 

 the Gotland strata then ought to be about 340 feet. Now the highest point deterrained 

 lies 261 feet above the sea, according to Steinmetz, near Rosendal in FoUingbo, and 

 there are thus nearly 80 feet unrepresented at that point. 



As may well be imagined, this uppermost stratum is highly variable as to its struc- 

 ture and organic remains. In some parts it well deserves its navne of crinoidal lime- 



') Silurlagren på Carlsöariie png. 17. 



