

AGE OF THE GASPE FORMATION 695 



Later the southern fauna found a way into New York through the Indiana 

 basin, but with only such slight admixture of species of the northern fauna as 

 could migrate southward in the Atlantic basin and enter through the Gulf 

 basin into the interior continental basin. 



The fundamental correlation principle involved in reaching the above con- 

 clusions is that the time relations of a fauna are indicated by its dominant 

 species. At any particular epoch the ancestors of all species which are to 

 become dominant in later ages were living, and in taking samples of a fauna 

 many forms closely related to later species may appear. The dominant ele- 

 ments of the fauna, however, express successful adjustment of the species to 

 the particular environmental conditions, both biological and physical, which 

 mark the epoch of such dominance. 



To use a familiar figure, the paleontological record is like a carpet, and the 

 particular species by which we recognize geological epochs are comparable to 

 the threads brought to the surface to make the local pattern. The individual 

 threads are long, however, and if we recognize them before or after the forma- 

 tion in which they form the dominant pattern it is a case of recurrence of the 

 fauna out of its typical time horizon. It is the particular combination of domi- 

 nant threads which makes up the pattern of each epoch as we know it, and by 

 which the epoch is to be recognized and correlated. 



Diastrophism undoubtedly is a fundamental cause in determining the par- 

 ticular pattern of the carpet at each stage in geological history. 



DISCUSSION 



REMARKS BY CHARLES SCHUCHERT 



Doctor Clarke and I together visited the Gaspe section, the only complete 

 one of the Lower Devonian in all eastern America. These formations rest on 

 the upturned black slates of the Ordovician, having about 2,000 feet of lime- 

 stones and 7,000 feet of sandstones. The section apparently begins with basal 

 New Scotland time, for here we collected Gypidula galeata and Leptwnisca 

 concava, and then the section continues unbroken into the Middle Devonian. 

 Above these Helderbergian limestones fossils are scarce until near the Grande 

 Greve horizon. In going along the bed of a small stream we were greatly sur- 

 prised to come upon large surfaces of a crystalline heavy bedded limestone, on 

 which lay Rhipidomella musculosa, Hipparionyx proximus, and Rensselwria 

 oroides, the three most typical late Oriskanian fossils. On my next visit I 

 located this horizon very exactly, and it is at the base of or even below the 

 Grande Greve zone. Collecting in this limestone reminds one strongly of the 

 true Oriskany of Albany county, New York. The Grande Greve limestone fol- 

 lows, and has many Oriskanian species — in fact, the fauna Is more decidedly 

 of this time than of the Onondaga, and yet there are reminders of this Middle 

 Devonian time. These limestones are followed by about 1,000 feet of sand- 

 stone in which no fossils occur, and then appears the York River fauna. AVhile 

 collecting these fossils one is impressed with their Hamilton aspect, and one 

 would make this correlation positive were it not for the presence of Rensselce- 

 ria ovoides gaspensis, Eatonia peculiaris, Leptoccelia flabellites, Chonostrophia 

 dawsoni, and Phacops correlator. Then all marine faunas cease, and the re- 

 mainder of the sandstone is probably of continental character. 



