208 REVIEWS 



Since the first of the century the quarrying industry of Maryland 

 has received attention incidentally from many different students of 

 geology. The various publications which have resulted from these 

 studies are summarized by Mathews in the first pages of the second 

 part of the report. Mathews considers the more important quarry 

 areas under the heads of (i) granite and gneiss; (2) marbles, serpen- 

 tines, and limestones; (3) quartzite and sandstones; and (4) slates and 

 flags. This classification is somewhat different from that followed by 

 Merrill in the first part of the report. 



In the treatment of each area the author gives a brief historical 

 sketch of the development of the industry, and a discussion of the 

 rocks as they occur in the quarry. In some instances the microscop- 

 ical and chemical analyses are given, and also the results of physical 

 tests, including a determination of the crushing strength, ratio of 

 absorption, specific gravity, and weight per cubic foot. The rock as it 

 occurs in the quarries and natural exposures ; the mineralogical com- 

 position and texture ; and the colors of the granite, limestone, marble, 

 serpentine, and sandstone, are well illustrated by cuts, photomicro- 

 graphs, and colored lithographic plates. 



The granites of Maryland are shown to be ordinarily schistose, and 

 mainly of a gray color. The granite from one or two of the quarries 

 is described as having a reddish or pinkish color, but possessing a por- 

 phyritic texture. In the case of the rock known as gneiss, occurring 

 in the vicinity of Baltimore, the color and texture vary with the alter- 

 nation of layers. In all cases the dimensions are controlled by joint- 

 ing planes, which strike in various directions, owing to which the stone 

 can often be used only for the smaller constructional purposes. 



The marbles and limestones of Maryland are the most widely dis- 

 tributed of all the building stones, and occur in most of the formations 

 from the Algonkian to the Triassic. The Cockeysville marble is 

 exploited the most largely, and is probably the best known of Mary- 

 land limestones or marbles. The Potomac marble is a conglomerate 

 with a striking color and' texture, and is the only stone of- this charac- 

 ter used to any extent in the United States. 



Serpentine has been quarried in several places, mainly for decora- 

 tive purposes. Dry seams have seriously interfered with the successful 

 development of this stone, and the quarries have been temporarily 

 abandoned. 



Sandstone is quarried extensively in only one locality, Seneca. The 



