GEOLOGY OF THE BROADALBIN QUADRANGLE 35 



lower Mohawk valley and is sometimes absent altogether, as at 

 Canajoharie. Around Little Falls the thickness is from twenty to 

 twenty-five feet, while in the Black river valley it shows a thickness 

 of fifty or sixty feet and is always present and characteristically 

 developed. 



Amsterdam limestone. The Amsterdam limestone, though gen- 

 erally under ten feet in thickness, appears to be very persistent over 

 the region and is usually easily recognizable both faunally and 

 lithologically. It comprises chiefly the pure, massive, gray, crystal- 

 line limestone which has been so much quarried in the district and 

 which directly underlies the very typical Trenton. This massive 

 limestone apparently continues eastward across the Saratoga sheet 

 and to Glens Falls where it is quarried as marble. The relation 

 to the Trenton is finely shown in Christie's quarry (at the map 

 edge) one-half of a mile east of Mayfield where three feet of heavy 

 bedded Amsterdam limestone is in contact with the Trenton. In 

 the Haines quarry (off the map) north of Mayfield fine large speci- 

 mens of the characteristic columnar coral (Column aria 

 alveolata) occur in the Amsterdam limestone. 



Within the quadrangle good outcrops of the Amsterdam occur 

 along the fault east of Mayfield ; in quarries one and three-fourths 

 miles southwest, three- fourths of a mile east, and two miles north- 

 northeast of Cranberry Creek ; in a quarry two miles east of Broad- 

 albin; one-fourth of a mile and one and two-thirds miles east, one 

 mile south, and one and one-half miles southwest of Galway. At 

 most of these places the overlying Trenton is shown. At the locali- 

 ties east of Cranberry Creek and Broadalbin the cup coral (Strep- 

 telasma) has been noted in the formation. 



Trenton limestone. This formation, which is clearly of lower 

 Trenton age, is easily recognizable by its lithologic character and 

 the abundance of its characteristic fossils. It always consists of 

 dark, thin-bedded, irregular, compact limestones with distinct shale 

 partings. The Trenton outcrops at all the localities above cited 

 for the Amsterdam limestone. In addition to these there is an 

 excellent exposure of about fifteen feet of Trenton along the creek 

 at North Broadalbin which is a fine place for collecting fossils. 

 Also in Christie's quarry, at the map edge east of Mayfield, there 

 is an excellent exposure showing three feet of Amsterdam lime- 

 stone capped by twelve feet of dark, thin-bedded Trenton with 

 distinct shale partings and here, too, is a good place for fossil 

 collecting. 



