Origin of the Pennsylvania Siliceous Oolite. 



263 



the Pennsylvania State College locality. A smaller spheruled 

 rock occurring in greater quantity contains about a half per 

 cent less of Si0 2 with more iron, alumina and magnesia. 



Without attempting to take up the origin of oolites in gen- 

 eral, however, I merely mention that two writers working 

 independently of each other have from the microscopic study 

 alone assigned the Pennsylvania oolite as due to direct deposi- 

 tion from the silica-laden waters of hot springs.* This con- 



Built-up chalcedony bowlders of the Pennsylvania siliceous oolite locality. — 

 -^g- actual size. Figs. ], ?, 3, 4, 5, supposed actual rim bowlders. Fig. 6, sup- 

 posed core bowlder. 



elusion is no doubt correct. A hand specimen found recently 

 consisting of spherules of small size up to pisolitic inter- 

 mingled with chalcedony-coated pebbles points to its truth. 



But probably the most convincing testimony to the existence 

 in the Calciferous of a limited area of hot springs from whose 

 silica-laden waters these siliceous oolites were deposited, lies in 

 the fact that in the limited oolite area and nowhere else in the 

 entire region are found in considerable number bowlders of a 

 built-up structure which may have formed the rims of hot 

 springs or geysers. Types are shown in figures 1-6 



*E. 0. Hovey, Geol. Soc. of Am., vol. v, 1893. Dr. W.. Bergt, Ges. Isis in 

 Dresden, 1892. 



