ANALYTICAL ABSTRACTS. 30 5 



result in extending the space taken by the comments beyond that required for 

 the summaries. However, when the points at issue are of general interest, or 

 fundamental importance, it is advisable to make comments and enter into 

 discussions, even if the space taken by such comments be greater than that 

 given to the summary of the original articles. In such comments neither 

 commendation nor censure will be made, but the aim will be to point out the 

 conclusions announced which fail of complete establishment, and the general- 

 izations which appear to go beyond what is warrantedjjy the facts published. 

 The purpose of indicating what appears to the editor as deficiencies of these 

 kinds is neither to put himself dogmatically in opposition to the statements of 

 the author reviewed, nor with the belief that his opinion has more weight, but 

 to direct attention to the questions involved, and in cases of doubt to keep 

 them open for farther study in the field and laboratory. 



Mills ' finds in the Sierra Nevada, unconformably below the Mesozoic, 

 eruptive granites and sedimentary slates and quartzites. The latter in places 

 rest and were probably deposited ujDon the granite, while in other places they 

 are contemporaneous and imbedded within it. The quartzites are held to be 

 silicified phases of the slates. These rocks in age may run from Archsean to 

 the Paleozoic and some of them may be early Mesozoic. 



Darton - finds Ordovician fossils in the cr3^stalline slates and schists of the 

 Piedmont plain of Virginia, these rocks having been previously regarded as 

 Huronian. 



Lesley ^ gives a summary sketch of the pre-Cambrian rocks of Penn- 

 sylvania, the facts being taken from the detailed state reports. The Highland 

 Belt of New Jersey and Pennsylvania ; the Reading and Durham Hills ; areas 

 in Chester, Bucks, Montgomery and Delaware counties ; and an area on the 

 Schu3dkill river are placed in the Archean. All are i^egarded as sedimentary 

 in origin, because of the presence of marble, apatite and iron ore. The newer 

 gneiss of the Philadelphia belt, the Azoic formations of York, Chester and Lan- 

 caster counties, and the South Mountain rocks are not definitely referred to 

 any system. The term Huronian must be used simply as a proper and private 

 name for a series of rocks exposed along a part of the northern boundary of 

 the United States. Should a similar series appear in some other region and 

 be called Huronian on account of the resemblance, the name would have no 

 value whatever ; unless we should imagine that in a so-called Huronian age 

 the whole surface of the planet was stuccoed with a certain formation ; and 



' Stratigraphy and Succession of the Rocks of the Sierra Nevada of California . 

 James E. Mills. Bull. Geol. Soc. of America, vol. 3, 1892, pp. 413-444. 



'^Fossils in the " Archaan'''' rocks of Central Piedmont Virginia. N. H. Darton. 

 Am. Jour. Sci., 3rd series, vol. 44, 1892, pp. 50-52. 



3 The Laurentia?i and Huronian jForniations, by J. P. Lesle}-, in A Summary- Descrip- 

 tion of the Geology of Pennsylvania, Vol. i. Rep. Penn. Geol. Sur., 1892, pp. 53-164. 



