TWENHOFEL: EXPEDITION TO THE BALTIC PROVINCES. 390 
coral masses. Some of them may also have been subsequently formed 
by the settling of the sediment over the coral ridges, which would 
remain rigid while that filling the basins on each side would settle. 
At any rate, few or none of these inclinations and undulations have 
any significance in connection with the stratigraphic relations. 
Among coral reefs the strata in the different channels are more or 
less isolated, and they would dip away from the reefs in a way that 
would appear to carry them far below other strata in the direction of 
inclination, and if this basin or synclinal-like structure could not be 
discerned the conditions would lead to divergent interpretations. 
I do not wish to argue that younger strata are not present in the south- 
eastern part of the island, nor that strata of the same age occur over 
all parts of the island. I believe the truth lies between the two 
extremes, but wish to emphasize the fact that in each of the channels 
between the reefs there will be apt to be a different lithology, a differ- 
ent structure, and a different fauna from that in any other channel. 
Since the rate of deposition in each channel will be different from that 
in another, it follows that strata of a certain time interval will lie in 
one channel at a higher or lower level than that of another channel, 
and each will be below the rock of the reef which represents the same 
time interval. 
That to a considerable degree, the conditions described represent 
those obtaining in the Gotland section I feel assured. These views 
open a most interesting field for investigation, which should be begun 
by a careful mapping of every coral reef which can be discovered on 
Gotland, and this should be followed by a careful study of the inclina- 
tions of the strata, and these should also be mapped in order to see 
the relation of these inclinations to the coral reefs. Then the deposits 
and fauna of each basin between the reefs should be studied in an 
endeavor to correlate the strata of the different basins. When this is 
done the controversy as to whether certain strata on one side of the 
island lie underneath or above certain strata on the other side will have 
disappeared, and data will have been collected upon which something 
besides hypothesis can be erected. The detailed work that Drs. 
Munthe and Hedstrém are doing is laying the foundation to the ulti- 
mate untieing of this Gordian knot of Baltic stratigraphy. 
