Geological Reports of the State of New York. 229 



4. The Trenton limestone is an important rock for its marble, 

 in Schenectady County, and particularly in Saratoga County. It 

 is a fine grained and durable stone. On one of the strata of it at 

 Glen's Falls on the Hudson, the upper surface contains marks 

 "like those produced in soft mud by drops of rain." — Report, p. 

 97, Mather. Ripple marks are shown on " brown sandstone on 

 the road from Cattskill to the Mountain House, one mile above 

 the toUgate." p. 85. The chloritic and talcose rocks of the west- 

 ern part of the valley of the Hudson, are considered by Prof. 

 Mather, as ^'- metamorphic with intrusive rocks interstratified :" 

 and he extends the metamorphic rocks into the western part of 

 New England, pp. 93 and 96. In this opinion he is opposed by 

 some of our distinguished geologists, and cannot be followed with- 

 out far more and much stronger proof than has yet been offered. 

 Indeed it seems obvious that the metamorphic theory is an easy 

 method of breaking down the usual distinctions of the rocks. A 

 fine section of the rocks -'from the summit of the Cattskill Moun- 

 tain, south of the Mountain House, to Cattskill Creek," is given 

 on pages 78-81, Mather. 



5. The report of the paleontologist contains very important 

 matter, and some interesting corrections. 



Mr. Conrad distinguishes our rocks of the Silurian system, '-for 

 the sake of convenience," into three subdivisions, the Lower, 

 Middle, and Upper, Silnria7i series ; it seems also to be quite a 

 natural arrangement. The danger is that the classification has 

 been made too early, and that adequate examination has not set- 

 tled the entire distinctness of all the series. A great proportion 

 of them however are satisfactorily ascertained. There is some 

 doubt about the termination upwards of the Loioer series. It is 

 limited by the Pentamerus oblongus lirnestone in the report, and 

 the lowest stratum in the Middle is made Rochester shale. If 

 we understand it, this Pentamerus limestone at Rochester is to- 

 wards the lower part of the shale, and at Lockport is found en- 

 tirely above the Rochester shale, which is much thicker there 

 than at Rochester ; there would be no ditfculty in the natural 

 arrangement in making the Red or Medina Sandstone the upper 

 stratum in the Lower Silurian. But the Pentamerus limestone 

 must go with it, in whatever series it is placed. 



On p. 31 is a tabular view of the whole series, with the cor- 

 responding rocks of MurchisoD, and the characteristic genera of 



