42 Field Columbian Museum — Geology, Vol. III. 



nodules are of a light cream color, with membranous patches of 

 red and brown dried organic matter, (Meloboesia) which continues to 

 produce the characteristic pungent odor of drying marine vegetation. 

 From the weights and dimensions of 56 individuals, the writer has cal- 

 culated the average size and shape. It is a rounded body, like a slightly 

 crushed sphere, 9.9 centimeters long, 8.7 centimeters wide, and 7.6 

 centimeters thick. • Its weight is 340 grams. The variation of size 

 in the nodules at hand is considerable, the maximum diameters of 

 the 56 individuals lying between 6.8 and 14 centimeters, and the 

 minimum diameters between 5.7 and 11.2 centimeters. The corres- 

 ponding weights are 118 and 940 grams. Between these limits the 

 sizes and weights of the nodules are distributed with a fair degree of 

 uniformity. While the individual nodules frequently depart far 

 from a true spherical form, they appear on casual inspection to do 

 so in all possible directions, and with no tendency toward any other 

 definite shape than the sphere. When the dimensions of all the 

 specimens are tabulated, however, it appears at once that the 

 majority of the forms are such that the three perpendicular axes or 

 diameters are unequal, and the length of the intermediate is an 

 arithmetical mean between the longest and the shortest diameter. 

 The average nodule, as described above, also has this form. Few of 

 the specimens depart far from these proportions. Many, however, 

 while maintaining their ratios between major, median, and minor axes 

 do depart materially from the form of the spheroid of the same axes. 

 One is in the form of a cone with a large, shallow depression in its 

 base, well to one side of its axis. (Plate XXVI, Fig. 6.) Others have 

 slight flattenings and concavities which are suggestive. Frequently, 

 on the flatter sides of the nodule there will be slight depressions a 

 little to one side of the centre. These forms dimly but persistently 

 suggest half-obliterated fofms of familiar gastropod shells. (Plate 

 XXVI.) 



The specific gravity of a specimen weighing 540 grams was 

 found to be 2.30.* 



The surface of the nodule (Plate XXV) is always of an irregularly 

 rough or warty appearance. It is composed entirely of the skeletons 

 of calcareous encrusting organisms which are chiefly 'corals, bryozoa 

 and algae. In places the surface is covered with cylindrical branch- 

 ing forms, (Madracis f ) which may attain a height of 8 mm. and a dia- 

 meter for individual cylinders of perhaps 2 mm. These forms were 

 all dead when the specimens were collected, and are in all instances 



* See p. 50 for cause of low results. 



