FOSSIL REEFS: CAMBRIC 417 



Fossil Coral and Stromatopora Reefs. 



Cambric and Pre-Cambric. The oldest reef-forming organisms, 

 the ArchcvocyatJiidcc, were originally referred to the sponges, and 

 more recently to the primitive perforate madreporarian corals, of 

 which group they probably form a distinct order. They have been 

 reported from a number of localities in the Cambric, including both 

 Western United States (California, Nevada) and the eastern part 

 of North America (Newfoundland, Labrador), Sardinia, Spain, 

 Northern Siberia and Australia. In a number of these localities 

 they have been found to constitute layers or strata of which they 

 formed the principal portion, but they did not build massive reefs 

 comparable to those of the present day. Since they were all simple 

 corals, and of a very porous character of skeleton, they were not 

 especially adapted to the formation of reefs. Nevertheless, they 

 constituted an important limestone builder of this period, forming 

 in the straits of Belle Isle, Labrador, beds of coral limestone 

 varying in thickness from 25 to 50 feet. In many cases evidence of 

 shallow water, such as conglomerates, ripple marks, trails, etc., are 

 found in association with the beds of Archseocyathidse. In Sardinia 

 (Bornemann) and in Australia similar extensive reefs of these 

 corals are found, in some cases extending up into the Ordovicic. 



The recent finding of archseocyathid fossils forming limestone 

 masses in the Animikie of Canada makes this one of the oldest if 

 not the oldest reef -building coral. The probabilities are that these 

 corals lived in shallow and comparatively warm waters. 



The Hydrocoralline, Cryptozoon, fornied an important reef 

 builder in the upper Cambric and lower Ordovicic of North Amer- 

 ica. It always occurs in layers which often have a considerable 

 extent. The individual heads are spherical, from i to 2 feet in 

 diameter, or plate-like, with a thickness of one or two feet, and 

 from 5 to 100 feet in horizontal extent. These are not reefs as we 

 apply the term to such structures in the modern sea, though super- 

 ficially they must have had the appearance of a platform of coral 

 heads not dissimilar to some parts of the broader portion of the 

 Great Barrier Reef of Australia. They may perhaps be referred to 

 as "bedded reefs," and their distribution is probably synchronous 

 with that of the stromatoporoid and other hydrocoralline genera. 



These types apparently also formed similar bedded reefs in the 

 pre-Cambric sediments of North America. Walcott has figured a 

 "reef" of Cr\ptozodn (?) frequens (?=:C. occidcntalc, Dawson) 

 from the Algonkian limestone (Ijelt terrane) of northwestern Mon- 

 tana, where it forms beds from 6 inches to 3 feet or more in thick- 



