No. 2385. CRYSTALLOGRAPHIC STUDY OF DATOIATE— SHANNON. 499 



temporaneous with the datolite. There was probably more or less 

 variation in the temperature and composition of the solutions from 

 cavity to cavity, but such variation was gradual and the total differ- 

 ences were small. This condition of affairs is represented in the 

 crystals by very gradual variation. Those of any one cavity are 

 identical in habit except for differences due to varying distortion 

 caused by interference of adjacent crystals during growth. Although 

 the crystals on different specimens commonly show distinct differ- 

 ences in habit, the variation is seen to be gradual when a large number 

 of specimens are examined. 



While the several types which have been described would be dis- 

 tinct and easily definable were only a few crystals, showing the 

 extremes of development at hand, the examination of such a large 

 number of crystals as has been accessible for the present investigation 



Fig. 24.— Clinographic projection of crystal 33 showing new forms h (461), e t (353), mi (12.25.1) 



T (351) AND 6 (343). 



reveals such a gradual transition from type to type through interme- 

 diate habits that the definition of types becomes futile. All of the 

 habits described by Kraus and Cook can be illustrated by crystals 

 selected from the series at hand. Their type 1 is by far the most 

 abundant habit represented at the locality. The forms noted by 

 them are all of common occurrence except the three forms which 

 they gave as new, ra y , 7i y , and n z . Numerous other accessory forms 

 were seen on crystals of this type, most of them being of infrequent 

 occurrence, as noted under the discussions of forms. Figure 3 is 

 given to show the general appearance of these crystals in orthographic 

 and clinographic projection. Such crystals are well illustrated iu 

 the photographs (pis. 104-105). From this typical development the 

 crystals vary in one direction by suppression of the basal pinacoid to 

 acute pyramidal types similar to type 2 of Kraus and Cook, as illus- 

 trated in figure 5. These crystals are commonly smaller and less 



