348 bulletin: museum of comparative zoology. 



knolls are called by the people "Klintar," and they constitute the 

 hearts of the elevations of the island. Probably the original summit 

 of every one of these reef masses has been eroded away, as well as later 

 rock which was deposited about their margins. In the cliffs the pecul- 

 iar forms developed in the coral masses have led to various legends, as 

 the "Old Man of Hoburgen," etc. Some of the coral colonies are 

 quite large. At Hoburgen a single stromatoporoid colony which shows 

 continuous growth, but has two included marl pockets, is ten and a 

 half feet wide and eight feet high. 



At Staffs klint, the reefs extend to and into the Marl shales, tend- 

 ing to show that at that place growth apparently was continuous from 

 the times of Marl shale deposition up to, and probably beyond, the 

 time of the deposition of the Spongiostroma bed, thus bridging the 

 gap between the upper and low^r divisions. 



Interpretation of the Gotland Section. 



Any interpretation of this famous section must recognize the 

 importance of the coral reefs. They control the present shore and 

 surface topography of the island and they must have exerted a large 

 influence upon, even if they did not control, sedimentation, during 

 the times of their development. ^Yhat were the conditions under 

 which they were built? It has been shown that at Hoburgen and 

 Staffs klint, and could be shown in many other places, that they 

 extend through many beds, and it is assumed that they grew more or 

 less continuously while the sediments were depositing around them. 

 A question of great importance in this connection is whether the rock 

 of the coral reefs is of the same age as that of the other beds which 

 at any particular level lie on their flanks. The conditions around 

 modern coral reefs help to solve this problem. These, at least in 

 many, and probably most instances, rise with steep slopes from 

 deeper waters "and if elevated above the sea, they would stand as 

 broad ramparts separated by passages mostly 20 to 200 feet deep." ^ 

 Vaughan describes a like bottom topography about the Florida reefs, 

 but the passages separating the reefs are "usually 9 to 12 feet" and 

 "always less than 10 fathoms." - The surface of a modern coral reef 

 is very irregular and " there are deep cavities among the congregated 

 corals, in which a lead will sometimes sink to a depth of many feet 



1 Dana. Coral and coral islands, 1800, p. 389. 



2 Vaughan. Papers Tortugas laboratory Carnegie inst. Washington, 1910, 4, p. 109. 



