350 A. W. GRABAU — SILURO-DEVONIC CONTACT IN NEW YORK 



lime in Erie county is, according to the measurements given by Bishop, 

 something over 50 feet, including the cement stratum. 



MA N L J I \s' L 1 .1/ ES TO .V E 



Occurrence and general character. This rock, the Tentaculite limestone 

 of most authors, is represented in Erie county by a stratum of limestone 

 locally known as the " Bull Head " rock. This stratum has a thickness 

 of? feet in North Buffalo and 8 feet at Williamsville and Akron. It 

 rests immediately on the Rondout Waterlime, the passage from the one 

 to the other being a gradual one. The rock is a dolomitic limestone of 

 a very compact, semi-crystalline character, with a high per cent of ar- 

 gillaceous material and not infrequently a strong petroleum odor. It 

 is mottled, having frequently the appearance of a limestone breccia, and 

 consists of purplish gray angular or rectangular pieces and similar light 

 colored and more yellowish ones. These latter appear to be more ar- 

 gillaceous than the former. Sometimes fragments of the purple rock 

 seem to be included in the yellow, while again in other cases the yellow- 

 ish rock is inclosed by the purplish. Careful examination of thin sec- 

 tions has not revealed any striking differences in character between the 

 two kinds of rock, except that the lighter colored portion is perhaps more 

 coarsely crystalline. The brecciation, if brecciation it is, is only marked 

 distinctly by the contrast in color between the two fragments, the rock 

 having otherwise a nearly uniform texture. The yellowish fragments 

 weather much more readily when exposed than do the purplish, the lime 

 being dissolved and an earthy residue remaining. 



This rock is commonly very porous in its upper portion, the cavities 

 being often lined with crystals of calcite or other minerals. The smaller 

 of the cavities are due to the dissolving out of the small coral Cyatho- 

 phyllum hydraulicum, which was exceedingly abundant in the upper 

 portion of the stratum. This coral has long been known, but has only 

 recently been described. Hall.* in 1843, stated that on Skajaquada 

 creek the upper portions of the Waterlime "abound with cavities, many 

 of them containing sulphate of strontian, but principally empty, and 

 showing the remains of a small coral, which has been partially removed." 



At Williamsville the rock is of a similar character ; u about 3 feet of the 

 upper part are unfit for burning, being too calcareous. Below this there 

 are 4 feet of good quality, and then a shaly mass of 2 or 3 feet thick- 

 ness, below which the rock is fit for cement." f About 8 feet of this 

 mass is referable to the Manlius limestone. 



At Akron the upper fossiliferous portion is more friable and earth) 7 , 

 and has frequently a strong petroleum odor. 



* Hall, 1S4:i, p. 171. 

 t Hall, 1843, p. 47(i. 



