178 Revieics — The United States Geological Survey. 



In AvchEean geology, Prof. Pumpelly has sturiied the structure of 

 the Green Mountain Range, which consists of a series of closely 

 appressed and overturned folds with a pre-Camhrian crystalline core, 

 and a surface of rocks apparently representing the Silurian, from 

 the Hudson River downwards, and the whole of the Cambrian, as 

 shown in Eastern New York. 



Dr. G. H. Williams has been at work on the crystalline rocks of 

 the Piedmont Region, in the Middle Atlantic Slope, and the volcanic 

 and other crystalline rocks about Baltimore. He has made out in 

 the volcanic rocks a sequence of basic, ultra-basic, and acidic erup- 

 tions, following each other in accordance with von Richthofen's law. 



At the other end of the scale, Prof. N. S. Shaler has been mapping 

 the morasses and superficial deposits of Massachusetts, Rhode Island, 

 and New Hampshire, and he estimates that nearly one-half of the 

 swamp areas in the United States, which by suitable treatment 

 may be made fit for agriculture, are to be attributed to the disturb- 

 ance of the drainage by the last Glacial Period. 



One distinctive feature of this report is the establishment of 

 a division of geological correlation, under the superintendence of 

 Mr. G. K. Gilbert. The specialists in each geological group or 

 system have to prepare essays on the present state of knowledge of 

 North American systems; on the principles of geological correlation 

 and taxonomy ; and on the possibility or otherwise of using in all 

 countries the same set of names for stratigraphical divisions smaller 

 than systems, from the American standpoint. Further, as the result 

 of a conference of the members of the Survey, an independent 

 system of nomenclature, of colours and conventional symbols for 

 maps, has been adopted. 



Of the papers or monographs accompanj'ing this report, the 

 principal is that of Mr. C. D. Walcott on the Fauna of the Lower 

 Cambrian or Olenellus zone, which has already been reviewed in 

 this Magazine. Another is that on the Morasses, etc., by Mr. N. S. 

 Shaler, and a third is an abstract of a report by the late Prof. R. D. 

 Irving and Prof. Van Hise on the Penokee iron-bearing series of 

 Michigan and Wisconsin. This series of rocks situated on the south 

 and west shores of Lake Superior, has a thickness of about 14,000 

 feet. It is placed by the authors as a distinct system, named 

 the Algonkian (=:Huronian), coming between the Cambrian and 

 Archaean. The lowest member of the iron-bearing series in this 

 region is a cherty limestone in which bands of white chert or quartz 

 are interlaminated with the limestone. The cherty material in some 

 places is 45 feet in thickness, and the silica varies from amorphous 

 to crystalline. One peculiar feature in this chert is the tendency to 

 assume a brecciated form, in which angular fragments up to 2 or 3 

 inches across are imbedded in chert of a precisely similar character. 

 Sometimes the brecciated portions are wholly included in the cherty 

 zone. Though no organic remains have been met with, either in the 

 limestone or the chert, the authors consider that both kinds of rock 

 are probably of organic origin, and they compare the chert with the 

 beds of the same material which in this and other countries have 

 lately been proved to be derived from organisms. 



