TWENHOFEL: EXPEDITION TO THE BALTIC PROVINCES. 343 
IVb. Ostracodan limestone, or marl shales and crinoidal limestone. 
IVa. Bottom stratum with Stromatoporan limestone and Spongio- 
stroma. 
III. Upper cliff level of varying composition in different localities. 
II. Lower cliff level. 
I. Stricklandinia marl.! 
Below the lowest visible strata of the northern end of the island are 
others which have been revealed by boulders on the shore near Visby. 
These consist of red shales containing the coral Arachnophyllum, on 
account of which they have been called the Arachnophyllum shales. 
Each of the above classifications is subject to the same criticism, 
in that divisions have been named after fossils which by no means 
always occur, or after some lithic characteristic which is only locally 
present. 
Attitude of the strata. 'This is the bone of contention over which 
opinion has clashed.’ In many places there appears to be a definite 
dip southeastward, but in an extremely great number of other places 
it can as definitely be determined that a pronounced dip in the oppo- 
site direction obtains. Since, however, the lowest visible division, or 
zone, is exposed only at the northern end of the western shore, near 
Visby, it appears reasonable to assume that there is a general gentle 
southeastward dip, from which, however, there are many reversals 
of inclination. The island of Storo Karlso excellently illustrates the 
directional variations of inclination. On the western side of the 
island the Marl shales are beautifully exposed to the south and north 
of the point on which the light-house stands and the beds dip into the 
sea. On the eastern side there are no exposures of the Marl shales, 
but overlying beds are extensively exposed and dip eastward into the 
sea, while on the coast of the main island directly opposite (Gotland), 
the Marl shales again appear with southeastward inclination (Plate 4). 
At the Lau Canal the beds dip northwest at an angle of about fifteen 
degrees. These facts bear but one interpretation, 7%. e., very little 
reliance can be placed on local inclinations in reaching conclusions 
relating to the general attitude, and from inclinations alone one can 
reach any conclusion desired, merely by selecting the proper place to 
reach the conclusion. 
Variation of sediments and faunas. There is nothing more striking 
in the Gotland section than the horizontal variation of the sediments 
and their contained faunas. These variations are to be seen in many 
1 Hedstrém. Guide book 11th. internat. geol. congr., 1910, no. 20, p. 8. 
