~<a eer 
58 The American Geologist. January 1902. 
The discussion of isostasy and crustal contraction (p. 48) and of 
the causes of glacial movement (p. 111) are the instances of this in 
the mind of the reviewer. On p. 99 the mean annual recession of the 
“Horseshoe Fall is placed at five feet. 2.18 ft. is the figure taken from 
those of the annual reports of the commissioners by Dr. Grabau (1901). 
An excellent bibliography is appended. The volume meets with a 
high degree of success in the modern requirements of instruction in 
the subject with which it deals. F. B. 
Geology of Rand Hill and Vicinity Clinton County, H. P. CusHine. 
(19th Annual Report of the State Geologist, New York State Mus- 
eum.) 
This report comprises an account of the geography of the district 
embraced by the Mooers Atlas sheet, a summary of its geologic his- 
tory, a detailed account of the crystalline formations, a discussion of 
the structural features of the Pleistocene deposits and topographic 
features and of the economic geology of the district. 
The oldest formation of the area is the Dannemora Gneiss; a 
Pre-Cambrian crystalline, granitoid complex the origin of which is 
not positively determined. Into this body have intruded gabbroitic 
and syenitic massifs—the gabbroitic massif comprises both noryte 
and the ‘‘anorthosyte gabbro”. The latter type is characterized by 
the predominance among the index minerals of labradorite (Ab, An,) 
In spite of the place which the term anorthosyte has won in petro- 
graphic literature it seems questionable whether the term should be 
allowed, by its retention, to perpetuate an early inaccuracy in the de- 
termination of the feldspar species. 
The analysis and recalculation of the anorthosyte-gabbro shows 
a considerable percentage (7.5) of orthoclase. This constituent is not 
mentioned in the petrographic description. It may be that the potash 
molecule is largely combined with the albite molecule. 
Later igneous intrusions in the gneiss are represented by syenitic 
and diabasic dykes. 
The Palaeozoic formations of the district are a coarse gritty sand- 
stone of the Potsdam age, a Calciferous dolomyte and a siliceous 
Chazy limestone. 
The region is considerably faulted, the most marked faults 
being the Cambrian sandstone and the Chazy limestone side by side 
There is no fault affecting the relationships of the Pre-Cambrian 
gneiss and the Palaeozoic sediments. The formations are excessively 
jointed, There are two sets of master-joints striking north and south 
approximately and northeast and southwest. 
The glacial deposits, both morainic and till, are widespread, but 
very irregular and evidently of considerable physiographic interest. 
There is little of economic importance in the formations of this 
district save a large amount.of good building stone. As is the case 
throughout the Adirondack region, the origin and correlation of the 
gneisses furnish at once the most important and most difficult prob- 
lem, F. B. 
