HANDBOOK FOR THE DEPARTMENT OF GEOLOGY. 541 



on samples from (1), Lake Umbagog, (2), Morris County, New Jersey, 

 and (3), Paper Creek, Maryland : 



Per cent. Per cent. Per cent. 



Silica 80.53 80.60 81.53 



Iron oxides 1. 03 3. 33 



Alumina 5.89 3.84 3.43 



Lime 0.35 0.58 2.61 



Water 11.05 14.00 6.04 



Organic matter '. 0.98 



Number 3 showed also small amounts of potash and soda. 



2. Calcareous group. — These rocks are made up of the more or less 

 fragmental remains of mollusks, corals, and other mariue and fresh- 

 water animals. Many of them are but consolidated beds of calcareous 

 mud full of more or less fragmentary shells or casts of shells as in 

 specimen No. 70169 from near Cincinnati, Ohio, and No. 36139, from 

 Rochester, New York. Others are composed wholly of quite perfect 

 shells as the well known "coquina" from near St. Augustine, Florida, 

 (specimen No. 26023. See PI. cxxiii). From such forms as these we 

 have all possible gradations to compact crystalline limestone. Such 

 gradations may readily be traced among the specimens exhibited. 



Special names are often given these calcareous rocks designating the 

 character of materials from which they are derived. Coral and shell 

 limestones, as the names denote, are composed mainly of the debris from 

 these organisms (specimens 70169, 36139, 35907, 70036, 38591, 25197, 

 and 35530). In the shell limestone (Lumaohelle) from the Tyrol (No. 

 38783) the pearly lining of the shells still retains its original beauty. 

 Shell marl is a loose, pulverulent earthy rock containing remains of 

 shells (specimen No. 36043 from Drayton Island, Florida, and No. 70034 

 from Australia). Shell sand is a loose aggregate of shell fragments 

 formed on sea beaches by the action of wind and waves (see specimen 

 Nos. 20250 from Bermuda, and 35811 from the Hawaiian Islands). Cri- 

 noidal limestone is composed mainly of fragmental remains of crinoids 

 (specimens Nos. 35791 from Ouondago County, New York, and 35801 

 from the Isle of Gotland). Chalk is a fine white rock composed of finely 

 broken shells of mollusks and other marine animals associated abun- 

 dantly with the minute shells of forarainifera (specimen No. 36013 from 

 England). Nummulitic limestone carries fossil nnmmulites as shown 

 in the specimens from the pyramid of Cheops, Egypt (Nos. 39165 and 

 26816). 



3. Carbonaceous group. — Peat, Lignite, Coals, etc. The rocks of this 

 group are made up of the more or less fragmental remains of plants. 

 In many of them, as the peats and lignites (specimens Nos. 70097 and 

 6962) the traces of plant structure are still apparent. In others, as the 

 anthracite coals, these structures have become wholly obliterated by 

 metaraorphisms, or, if observable at all, are to be seen only with a 

 microscope of high power. Such belong properly in the group of ineta- 

 morphic rocks. 



