REPORT OF THE SECRETARY. 9 



discovered. The species which were collected proved to be of such typical 

 Trenton forms that there could be no doubt of the Middle Ordovician age of 

 this particular shale. Limestones known to be much older outcrop so short 

 a distance to the east of this that a great fault or displacement between the 

 two kinds of rocks is clearly indicated. 



With these facts in hand, the fault was traced for a distance of 30 miles 

 north and south, thus again showing that the graptolites proved the key to the 

 geologic structure of the region. 



EXPLORATIONS IN THE OHIO VALLEY FOR FOSSIL ALGAE AND CORAL REEFS. 



Through the extensive studies of the Secretary for several years 

 past, the collections of the National Museum are rich in limestone- 

 forming pre-Cambrian algae — a low order of water plants that 

 secrete lime or silica. An instructive series of these fossils has been 

 placed on exhibition, but in order to show the geologic occurrence 

 and evolution of this group of plants it was necessary to supplement 

 the pre-Cambrian forms with specimens of more recent age. Ac- 

 cordingly Dr. R. S. Bassler, curator of paleontology, spent some 

 weeks in the Ohio Valley, particularly in the blue grass region of 

 Kentucky, in a search for large exhibition specimens, and in a study 

 of their mode of occurrence. He was successful in procuring a num- 

 ber of showy exhibition specimens as well as numerous study collec- 

 tions. 



More difficult, however, was the discovery and quarrying of a 

 fossil coral reef suitable for exhibition in the Museum. Coral reefs 

 are known at several horizons in the Paleozoic rocks of the Ohio 

 Valley but they are seldom so exposed that an instructive section 

 can be quarried out without injury to the specimens. A great reef of 

 corals outcrops in the strata along the banks of Chenoweth Creek at 

 Jeffersontown, near Louisville, Kentucky, and this was selected to 

 furnish an exhibit for the Museum. A section of the stratified rocks 

 6 feet by 10 feet was bodily quarried out of the bank, and these strata 

 with their contained corals were later set up in the exhibition hall of 

 paleontology. 



The lowest layer of limestone is composed largely of fossil brachi- 

 opod shells. Next above is a layer with scattered corals belonging to 

 a long-tubed species {Columnaria caleina Nicholson), probably torn 

 by waves from a near-by coral reef. Overlying this is a limestone 

 stratum largely made of the twiglike stems of stony Bryozoa (Tre- 

 postomata). 



The main reef of corals is chiefly composed of the rounded heads 

 of three species of honeycomb corals, some with radial partitions in 

 the tubes {Columnaria alveolata Goldfuss), others without such par- 

 titions {Columnaria vacua Foerste), and still others with spongy 

 walls (Calapoecia cribriformis Nicholson). Large stems of fluted or 



