The Black Naples Shales (Gardeau shales). — These arc 

 highly bituminous, dark brown or black shales, with a 

 chocolate colored streak. They split into thin layers, which 

 often have iridescent surfaces. When struck with a hammer 

 they emit a strong petroleum odor. The joint fissures are 

 well developed, two sets usually being recognizable. These, 

 together with the fissility of the shales, often give the cliff 

 the appearance of having been cut up artificially, smooth 

 walls, projecting prisms and parallelepipeds resulting, while 

 deep fissures frequently penetrate into the rock. Fossils are 

 rare and consist mainly of plant remains, commonly in an 

 unidentifiable condition. 



This rock forms the walls of the gorge for many miles 

 above the bridges, the lower strata having entirely dis- 

 appeared beneath the bed of the stream. The black shale is 

 succeeded by olive shales, some of which are more sandy 

 than others, but all are quite destitute of fossils as far as 

 known at present. Without doubt, however, diligent search 

 will reveal an interesting, though limited fauna, probably 

 containing a number of fish remains. 



Although the rock is generally deficient in calcareous 

 material on account of the scarcity of fossils, such material 

 does occur at intervals in the form of calcareous concretions. 

 These are often of great size — sometimes eight or ten feet in 

 diameter, but usually much smaller. They are commonly 

 lense shaped, though gobular or loaf shaped forms are not 

 uncommon. Imitative forms of grotesque appearance are 

 frequent. The stratification is sometimes continuous 

 through them, at other times the strata bend over and 

 under them exhibiting a crowded appearance, as if the 

 growing concretion had forced them apart. It is probable, 

 however, that the concretion was fully formed before the 

 lithification of the adjoining strata had taken place, and 

 that on the contraction of the rock consequent upon lithifica- 

 tion, the strata settled down, and produced this crowded 

 and bent appearance. The source of the calcareous material 



