CANANDAIGUA AND NAPLES QUADRANGLES 41 



n o s u s Conradj Hipparionyx proximus Vanuxem, 



Meristella lata Hall, Chonostrophia complar 



n a t a Hall, etc. A few Imperfect fossils have been found in the 



outcrops on Flint creek near Phelps Junction but mostly when the 



rock takes on the form of a thin quartzite or breccia as here it is 



devoid of fossils. , 



Onondaga limestone 



Throughout the exposures of this rock fossils are abundant but 

 they, are not easily obtained because of the difficulty in setting 

 them free of the matrix. Experience has shown that the endeavor 

 to acquire the remains from the unweathered exposures is for the 

 most part fruitless as Avell as arduous except where there are shale 

 masses intercalated between the limestone beds. The fauna is 

 specially profuse in corals but the agglomerations of these or- 

 ganisms which are seen in the lower beds of this district become 

 immense coral plantations farther westward in the vicinity of 

 Leroy, Genesee eo. Nature has helped to solve the difficulties at- 

 tending the extraction of these fossils by scattering over the 

 county and through the soil southward innumerable blocks of 

 this rock. The corals are partially silicified in the bed and on 

 exposure become more so and the dissolution of the calcareous 

 matrix makes the occurrence of silicified corals of this formation 

 extremely commion over much of the region covered by this map. 

 The layers of the limestone that are associated with and more 

 or less impregnated by the chert, weather into all sorts of irreg- 

 ular shapes according to the degree of dissemination of the lime 

 throughout them and when this silicious rock has become 

 thoroughly " rotten," that is, has lost all its lime, the silicious 

 residuum retains with minutest precision the imi>ressions of the 

 organic contents. By the examination of such masses of rotten 

 stone has the fauna in an important degree been made out, and an 

 illustration of their significance is iseen in the fact that these 

 masses from Ontario county produced specimens of trilobites 

 ak)ne of which 55 drawings were made for the monograph of these 

 organisms published as volume 7, Palaeontology of New York. 



In these weathered blocks students of this fauna will find their 

 inat(»rial in most suitable form for study; these will not however 



