GEOLOGICAL SCALE AND STRUCTURE. 17 



found in the Castalia Springs of Erie county. The Castalia Springs are, 

 in reality, the point of exit of a large volume of under-ground drainage. 

 For fifty to seventy-five miles to' the southward there is an entire absence 

 of surface streams, all the water descending promptly through the joints 

 of the limestone, which is here covered with but a shallow deposit of 

 drift. 



The Lower Helderberg formation undoubtedly gives rise to the oil 

 rocks of Petrolia, Canada, and of the immediate vicinity. It unquestion- 

 ably, also, contains many of the salt deposits of that portion of the 

 country, which have been in past time referred to the Salina age. 



A single other element remains to be inserted in the Lower Helder- 

 berg column, the interpolation of which, at this point, may occasion sur- 

 prise to those who are conversant with the older statements in regard to 

 our geological scale. The element to which reference is here made is 

 known as the Sylvania sandstone. A remarkable series of deposits of 

 extremely pure glass sand has long been known in Lucas and Wood 

 counties of northern Ohio and in adjacent territory in the state of Michi- 

 gan. The two best known of the Ohio deposits are those of Sylvania and 

 Monclova, which respectively lie ten miles northwest and west of Toledo. 

 Other similar deposits are known in Wood count}^. Since the develop- 

 ment of the glass industry in northwestern Ohio, following the discovery 

 of natural gas in that region, these sand deposits have been worked on a 

 very large scale in meeting the demands of this new interest. The sand 

 affords a basis for the manufacture of glass of the highest quality. In the 

 Sylvania quarries the sandstone is found twenty or more feet in thickness, 

 and resting upon beds of normal Waterlime, which is exposed a few rods 

 to the eastward. The entire series is sharply inclined here, descending 

 in almost a due west direction at the rate of one foot in seven. The 

 rocks overlying the sandstone, as observed in extensive quarries that are 

 open here, are unmistakable Waterlime, or Lower Helderberg, containing 

 all the characteristic marks of the formation, including its chemical com- 

 position, its bedding, its bituminous streaks and its fossils. Further on, 

 the conglomerate phase of the Waterlime, described on the previous page, 

 appears. There is nothing in the whole formation more characteristic 

 than this. At the end of the series, eighty rods to the westward from the 

 sandstone quarry, a few feet of undoubted Corniferous limestone occur, 

 rich in the fossils of the formation and true to its chemical composition. 

 These facts are absolutely decisive as to the age of the sandstone. It lies 

 at least two hundred feet below the Corniferous limestone. 



The Monclova or Holland sandstone apparently holds a like position 

 in the series to that of the Sylvania sandstone. The Grand Rapids sand- 

 stone of Wood county probably belongs to the same horizon. Again, it 

 is presumably the Sylvania sandstone that was reached in the deep wells 

 of Cleveland and Wadsworth within the last four years, at a depth of 

 over two thousand feet below the surface and under cover of three hun- 

 2 G. O. 



