GEOLOGY AND PALEONTOLOGY OP THE SCHOHARIE VALLEY 153 



Becraft limestone 



Scutella and Eiicrinal limestones [Vanuxem etc.], Sparry limestone 

 [Gebhard], Upper Pentamerns limestone, Upper member of the Deltbyris 

 shaly limestone [Matlier], Upper limestone of Becraft mountain 



This limestone was included by Mather in his Delthyris shaly 

 series, but has always been treated by subsequent authors as a 

 separate formation. Its best exposure is on Becraft mountain 

 near Hudson, where it is 45 feet thick and extensively quarried at 

 the present time and manufactured into Portland cement. 



Lithically the rock is a coarse-grained crystalline lime sand- 

 rock, densely packed with brachiopod shells, so that not infre- 

 quently it has the character of a shell rock or coquina. This char- 

 acter is well shown on the weathered edges of the rock, where 

 the shells stand out in relief, as shown in the photographs 

 [pi. 13, 14]. The rock is massive bedded, compact and hard, and 

 when fresh of a dark gray color, but weathering Creamy or white. 

 The lower part is rich in joints of crinoid columns, which are 

 also frequent throughout the mass. The basal portion of a large 

 crinoid, Aspidocrinus scutelliformis is common in 

 the lower part. The fancied resemblance of these fossils to the 

 echinoid Scutella has given rise to the term '' Scutella limestone ". 

 These calyx bases are from one to two inches in diameter, gen- 

 erally flatly bowl-shaped, though sometimes having more the 

 shape of a very flat cone, with an apical aperture. The whole 

 shield is rendered crystalline by secondary inflltration of calcic 

 carbonate, as is usual in echinoderm remains, and the cleavable 

 calcite masses thus produced are very characteristic and easily 

 recognizable. They form a good index to the formation. On the 

 weathered surfaces these basal shields often stand out in relief 

 and in such cases their true form and character can be Avell seen. 

 In the lower and middle portions of the rock the shells composing 

 it are mainly Spirifers and rhynchonelloid brachiopods. In the 

 upper portion however Sieberella pseudogaleata 

 [fig. 74], the index fossil of this formation, predominates. 



From its resistant character this limestone mostly forms cliffs, 

 which are often very pronounced and generally project above the 



