366 RANGE AND EXTENT. 



and well characterized. At Colchester depot, and also for a mile northwesterly, the same 

 rock occurs, dipping east. It is slightly micaceous. Near the north line of Colchester 

 the same rock is found. It is separated from the noi'thern deposit of Georgia slate by the 

 Eolian limestone, which is nearly as dark in color as the slate itself. The relations of this 

 band of slate with the Georgia slate in Milton require further investigation. 



The first prominent feature in the Franklin County range of Georgia slate is Cobble 

 Hill, in Milton. It is entirely composed of clay slate, according to Professor Thompson. 

 The peak rises very abruptly from a plain, very similarly to Snake Hill, in the north 

 part of the town, which is capped by a different kind of rock. 



North of J. Barnes' house, in Colchester (near the tertiary deposit), and upon the north 

 town line of Colchester, on the Checkerberry Village road, tnere are ledges of clay slate. 

 There is some limestone, also, at the west foot of Cobble Hill. 



West of Checkerberry Village, upon the south bank of the La Moille River, at the first 

 bridge, there is a slate of a loose texture, cleaving naturally into " long two-edged or knife- 

 shaped fragments." In the north part of Milton, west of Snake Hill, the rock approaches 

 more nearly to roofing slate, and is largely developed, occupying a wide area upon Section 

 XI. It is developed still more finely in Georgia, and northwards. The trilobites, Bar- 

 randia Thompson^ etc., are found at the extreme western border of the slate, at Mr. H. 

 Parker's house, when the rock is a micaceous sandstone. The width of the slate in Geor- 

 gia is less than two miles. There is a fine exposure of clay slate near the intersection of 

 the Vermont and Canada Railroad with the south toAvn line of St. Albans. 



In the principal street of St. Albans there is a ledge of argillo-micaceous slate, belong- 

 ing to the Georgia slate group. Most of it has been removed for the benefit of travelers. 

 This slate passes northward, and an arm extends southward east of Aldis Hill, nearly to 

 the south line of St. Albans. The length of this arm is less than three miles. 



The conglomerate composed of pebbles of limestone, which was described as one of the 

 varieties of the Georgia slate, forms a marked feature in the aspect of the rock. The slate 

 increases in width north of St. Albans. Its trend is now a little east of north, extending 

 to the provincial line. Rice Hill, in Swanton, is composed of clay slate. The last ap- 

 pearance of the Georgia slate in Vermont is in the east part of Highgate, and the Avest 

 part of Franklin. Details respecting its minute features will be found upon Section XIII, 

 and there are particulars relating to the rock, not specified here, upon Sections XI. 

 and XII. 



Upon applying the usual rules for obtaining the thickness of strata by calculation, to 

 the slates in the north part of Georgia, the result shows that the total thickness of the 

 Georgia slate is at least 3000 feet. If it is folded once, the actual thickness would be one 

 half as great, viz., 1500 feet. 



The southern deposit is much thicker, though it may be reasonably doubted whether 

 we are yet sufficiently acquainted with the true position of the strata, or of the number of 

 the folds, to justify us in announcing conclusions. It is very certain, however, whatever 

 view may be taken of the age of the Georgia slate, that its thickness is much greater than 

 that of any well determined deposit of the Hudson River group ever yet described. Em- 

 mons calculated the thickness of the same terrain in New York, and found it to be as 

 great as 25,000 feet. This was upon the supposition that none of the strata were repeated, 



