44 G. E. Curtis — Theory of the Wind Vane. 



Washington County, of Virginia. This space of limestone and 

 calcareous shale marks the course of deep water during the 

 long early part of the Umbral, which seems to be represented 

 by very little material of any sort in the greater part of Penn- 

 sylvania. 



The limits of this area appear to be well-defined in south- 

 western Virginia. Eastward the great mass of limestone and 

 calcareous shale disappears within 8 or 9 miles, for not a bit of 

 it was seen along the Walker Mountain fault, nor is there any 

 along the Saltville fault in Bland County. At 50 miles to- 

 ward the west, in Pennington's gap through Stone Mountain, 

 the whole thickness of calcareous beds is barely 400 feet, and 

 a great part of that hardly deserves the name of calcareous 

 shale. This certainly indicates a shore not far away in Ken- 

 tuclcv, and leads at once to the conclusion that the Appalachian 

 gulf was greatly narrowed along the present southern line of 

 Virginia. The area of deep water extended almost north and 

 south until near the southern boundary of Virginia, where it 

 was turned slightly toward the southwest, and there its width 

 could not have exceeded 75 miles. Its direction was more 

 nearly coincident with that of the Cincinnati axis than with 

 that of the Blue Ridge region. 



The Lower Carboniferous was closed by a gradual silting up 

 of the gulf, a preparation for the Upper Carboniferous. 

 Throughout the whole area of Pennsylvania, Maryland, West 

 Virginia and Virginia, this upper division of the Umbral is a 

 mass of shales and sandstones with rare and thin streaks of im- 

 pure limestone in the more westerly portions of the area. In 

 many localities the passage from the Lower to the Upper Car- 

 boniferous is indefinite, as the lower plate of the Quinnimont 

 group or Lower Coal Measures is absent; but for the most part 

 the plane of separation between the two divisions of the Age is 

 sufficiently distinct. 



Art. VI. — The Theory of the Wind Vane; by George E. 



Curtis. 



The common weather-cock, or wind-vane, is no doubt the 

 oldest, as well as the simplest, of meteorological instruments. 

 In its earliest use, as a popular indicator of the weather, 

 erected at the summit of a flag staff or a church tower, or, in 

 New England, forming the usual apex of the town liberty pole, 

 the vane assumed the form of a cock, a fish, a trumpeter, or 

 other ornamental device ; but, with its application to accurate 



