ANALYTICAL ABSTRACTS. 865 



ures from this dip. Five beds of coal are recognized, two of which- — the 

 Bevier and the Mason City beds — can be profitably worked. The former of 

 these is the most important. Its estimated available tonnage within the limits 

 of this sheet is 336,000,000 tons. 



The report on the Quaternary geology is by Professor Todd. Three 

 divisions are noted, viz.: 1. Pre-glacial or basal clay, a light gray 

 clay, without northern pebbles, and of no great surface extent. 2. Drift or 

 till. The erratics comprise granites, greenstones, and a red quartzite identical 

 with the Sioux quartzites. The last seems not to be distributed much further 

 east than the area of this sheet. 3. A gray, loamy clay, which is intimately 

 mixed with fine sand, and contains a few well-worn pebbles and calcareous 

 concretions. This formation is McGee's "gumbo." Professor Todd con- 

 siders it the equivalent of the higher loess into which it appears to grade. 

 Much detailed information is given by Professor Wheeler concerning the 

 economical values of clays and shales of the region. 



The rocks present in the area covered by the Iron Mountain sheet are, 

 1) crystalline, massive Archean rocks, which are divisible into basic eruptives, 

 occurring in the form of dikes, and acid eruptives, including both granites 

 and porphyries ; 2) crystalline stratified Algonkian rocks, chiefly conglomer- 

 ates and slates, including the iron ore bed of Pilot Knob ; 3) clastic Paleozoic 

 limestones and sandstones. The economic interest of the region centers 

 chiefly in the iron ores and building stones. Thorough exploration has shown 

 that the Iron Mountain ore deposit is practically exhausted. The same may 

 also be said of the Pilot Knob deposit. 



H. B. K. 



The Granites of Cecil County in Northeastern Maryland. By G. Perry 



Grimsley. (Jour. Cin. Soc. of Nat. Hist., Vol. XVII., Nos. 1 and 2, 



April, July, 1894. Thesis for Doctorate, Johns Hopkins Univ.) 



The rocks of this region are holocrystalline with a northeast strike and a 



highly inclined dip to the southeast. The rock is of a light color with dark 



biotite arranged in more or less parallel lines. This foliation runs northeast 



while the dip is nearly vertical. Toward the gabbro contact on the north 



the feldspar of the granite is replaced in part by hornblende and biotite along 



with an increased amount of magnetite. Near the contact, bowlders of 



sheared and squeezed chloritic rock occur, together with dark oval patches of 



basic constituents. The latter are considered basic segregations rather than 



inclusions of foreign rock. Other rock types are diorite and staurolitic mica 



schist. 



As a result of dynamic action, old minerals have been more or less meta- 

 morphosed and new ones developed, with the production of a secondary foli- 

 ated structure. Of new minerals epidote is especially well developed. In 



