FCONGL. SV. VET. AKADKMIENS HANDLINGAR. I5AND. 19. N:<) 6. 7 



strata of thinbedded limestone and shale are intei'posed, north of Grötlingbo and Rone, and 

 they pass gradually upwards into the more uniform, härd crinoidal limestone. In the South 

 of Gotland again, wherever the sandsfone prevails, the intermediate stratum is oolite. 

 According to what has now been adduced, we have, from their petrographic cha- 

 racter, three strata viz. 



1. The oldest shale or sandstone stratum, in the following signed a. 



2. The laminar limestone, intermingled with shale in the north, beds of oolite or 

 pisolite in the south, signed b. 



3. The highest limestone; covering all the other strata, signed c. 



Along the east coast of Gotland this succession of the strata is somewhat ob- 

 scured through frequent dips and contortions of the beds. In how far thesc three 

 different strata can be well distinguished by their faunas, is at present, when so few 

 groups have been raonographically worked out, too early to decide and cannot be finally 

 settled until the rich Silurian Fauna of that island will have been described through 

 all its classes. 



Regardinff the chief characteristics of the different strata the followinff remarks 

 may serve. 



Stratum a. The thickness above the sea is extremely variable, owing to the 

 many curvatures and domeshaped folds into which it has been thrown. Near Halls 

 huk the shale is 50 feet thick, in Fardhem at Burge again it is found at 70 feet 

 above the sea level and at Alfva saw mill even at 80 feet. But it is probable that 

 its total thickneas is still larger, as shale beds are met with in Follingbo at a height 

 of more than 100 feet. The bottom of the harbour of Wisby at a depth of 20 feet, has 

 been found to consist of shale, and consequently this rock attains there at least that 

 amount of thickness below the level of the sea. Owing to the curvatures in this 

 stratum it is, however, very questionable whether these 20 feet are to be added to 

 the amount found in Follingbo. The sandstone south of Bursvik is not by far so 

 thick, only 20 feet at the inost. But the mäss hidden in the sea is probably far 

 thicker, as, owing to the southeastern inclination of the strata, only so little is visible. 

 Fossils are found cast ashore on Norderstrand near Wisby, enclosed in a soft, red 

 marly limestone. They are partially of the same species as in the gray shale but also 

 of characteristic forms. There is a low depressed variety of Goniophyllum pyramidale, 

 Phacops elliptifrons, a small Caraerella, but also Arachnophyllum typus which never 

 occurs in any higher stratum. This red marl is in all probability the basis of the oldest 

 and lowest shale beds of Gotland and to be found in situ deeper in the sea, from where 

 fragments are thrown up. Hitherto the oldest shale beds have only been found north 

 of Wisby. Through the presence of Stricklandinia lirata, Euomphalus Gotlandicus, Pleu- 

 rotomaria qualteriata var. and a species of Harpes, only found there, they announce 

 their age as Upper Llandovery. Stricklandinia does not occur higher up in the shale 

 beds. The beds above its zone, as well as the sandstone in the south, may be regar- 

 ded as of Wenlock age. Sections of this stratum are also seen in several places on 

 the east coast of Gotland as at Slite, Östergarn, though raixed up there with bands 

 of härd crystalline limestone. 



