CALCAREOUS ALGAE OF THE MIDDLE EAST 97 



and Distichoplax. Most of these were nodular or crusting forms, forming an 

 appreciable volume of the actual reef-structures and plastering the reef-fronts in the 

 surf zone. These two different environments, favoured by the green and red algae 

 respectively, are strikingly demonstrated by an analysis of Palaeocene-Lower 

 Eocene algae from Iraqi Kurdistan. Of 92 samples selected as showing well- 

 preserved algae, from localities all along the mountain arc from Banik in the north to 

 Sirwan-Balambo in the east, 67% show green algae only, 29% red algae only, and 

 only 4% a mixture of the two. Moreover, in the mixed samples one or other group 

 was a worn minority in each case. The preponderance of green-algal, back-reef 

 samples is perhaps to be explained by the inclusion of samples from intertonguing 

 Kolosh Formation, where only green algae occur, but there is no doubt in which 

 environment any particular sample originated. At some localities, e.g. Sirwan- 

 Balambo, red and green algal samples alternate, reflecting the former shifting reef 

 and shoal pattern through time at the spot now arbitrarily revealed as a cliff-section ; 

 at others, e.g. Koi Sanjak and Kashti, green and red algae predominate respectively. 

 These differences reflect local aspects of a palaeogeography not known in detail, but 

 emphasize the mutual exclusiveness of the two environments. 



In southwestern Iraq the desert outcrops of the Palaeocene Umm er Rhudhama 

 Formation reveal a different picture. This was a more gently-sloping, non-orogenic 

 shore of the Tethys than the opposite coast described above for Kurdistan : the 

 sea extended as a shallow sheet of water on to the slopes of the Arabian landmass, 

 and sedimentation was slow. The algae are abundant ; although abominably ill- 

 preserved, almost all are dasyclads, and there are no red algae at all. This was a 

 shallow-water coast with frequent sheltered bays with limy bottoms on which 

 spreads and thickets of dasyclads proliferated : it is a much less rich flora than that 

 of Kurdistan, and presumably provided few micro-environments like those of the 

 Kurdistan shoal-belt. 



Summarizing, with Dasycladaceae especially in mind, the principal kinds of 

 marine algal associations in the Middle East Tethyan rocks examined indicate : 



1. Reef and shoal environments, mostly exposed to rough surface water, or tide- 

 or current-swept. The home of nodular or crusting algae (Solenoporaceae, Coral- 

 linaceae and the problematic Lithocodium) , with dasyclads extremely rare. 



2. Fore-reef or seaward shoal-slope deposits. Much debris from the environ- 

 ments of category 1, as well as some indigenous non-dasycladacean algae, and only 

 exceptionally dasyclad debris from elsewhere, depending on current-patterns and 

 sediment-transport . 



3. Calm lagoonal waters behind reefs and similar barriers. Abundant Dasy- 

 cladaceae and Codiaceae, few other calcareous algae, with burial on the site of 

 growth, and only exceptionally current-transport to category 2. 



4. Calm coastal bays and similar shallow, largely land-locked waters. Dasy- 

 cladaceae and Codiaceae as in category 3. Burial on the site of growth, occasional 

 current transport to category 2, and much contribution to category 5. 



5. Neritic deposits out to sea on coastal shelves. Much sedimentation of broken 

 littoral and sublittoral algal skeletal remains, largely dasycladacean, as a con- 



