PORTAGE AND CHEMUNG GROUPS. 191 



distinct : in the upper part it is diagonal, a fact which may be used for determining the po- 

 sition of this mass at distant points. The diagonal stratification (fig. 31) prevails in the 

 Catskill mountain rocks, but has not been observed below the Chemung group. 



At Ithaca and Cortlandville, the lower part of the Chemung group is represented in the 

 green slates and flags. At the former place they are exposed in the cuts of the inclined 

 plane, while the Portage group is below, rising from fifty to one hundred feet above the 

 lake. At Cortlandville, the Ithaca group is exposed in the quarries about half a mile south 

 of the village. The same species of fossils have been found here as at Ithaca, namely, the 

 Microdon bellistriata ; a flat coral ; an ornamented univalve, which appears to be a Mur- 

 chisonia. The series ascends to Virgil. Here is a full development of the Chemung rocks. 

 It would seem, from a comparison of facts developed by a careful examination, that the 

 Ithaca group is not equivalent to the Chemung as it is developed at the Chemung nar- 

 rows ; but rather that is beneath, and situated between the Portage and Chemung groups. 

 There is, however, no necessity for separating the Ithaca from the Chemung group : it is 

 more simple to regard the masses as parts of one series, in which the inferior and superior 

 may differ in many points. According to this view, the rocks of Virgil and Chemung be- 

 long to one and the same age, and those of Cortlandville and Ithaca to another ; and this 

 view is borne out by the fossils collected at both places. 



Springs and mineral contents of the group in tlie central counties. The springs which 

 issue from the upper part of the Chemung rocks, are comparatively pure ; those of the 

 Genesee slate, may be bituminous. In a hilly region, numerous streams, originating in 

 springs, are expected ; in the valley of the Genesee, however, adjacent to the great gorge, 

 very few exist. The traveller, passing over the fine road from Mountmorris to Portage, will 

 be surprised at not meeting more than one or two small streams the whole distance. This 

 scarcity of running water is a great inconvenience to farmers, inasmuch as frequently it is 

 difficult to procure water for cattle. Cisterns and wells are the only modes left for fur- 

 nishing a supply, which of course becomes precarious in dry seasons. The nature of the 

 rocks, their porosity, and especially the deep cut of the Genesee river, combine in their 

 effects to produce a very thorough draining of a very wide extent of country on both sides 

 of the gorge. Still where there is a deep soil, upon a surface only moderately steep, the 

 drainage is not so perfect as to lay the upper parts dry ; and where a clay forms the sub- 

 soil, draining in the usual way may still be required. 



The minerals of the group have no claim to a special consideration : pyrites, in the 

 shale, is the most common ; it is the source of the chalybeate waters, wherever they exist 

 in the formation. Its presence aids the decomposition of the slates, facilitates first their 

 disintegration, and finally perfects those changes which end in a thorough separation of 

 the elements of the rock. 



