462 H. B. PATTON — THOMsONITE, MESOLITE, AND CHABAZITE 



tli e Table mountains, with their basaltic caps and a much more detailed 

 description of the various zeolitic minerals contained in the amygdaloidal 



cavities. They also discuss the results of the investigations of Professor 

 Carl Klein on the optical anomalies of analcite and apophyllite from 

 this locality.* 



During the past two years the Colorado State School of Mines, located 

 at Golden, has been conducting quarrying operations for the purpose of 

 securing for its mineral cabinet specimens of these Table Mountain zeolites. 

 A new locality opened up on the east face of North Table mountain proved 

 to be very prolific of these zeolites and produced man}' specimens of ex- 

 treme beauty. 



In most respects the zeolites here developed correspond closely with 

 the occurrences described in the above mentioned paper by Cross and 

 Hillebrand, and it is hardly worth while to duplicate what the}' have 

 already written on the subject. The minerals thomsonite and mesolite, 

 however, not only show extraordinary beauty, but occur in a great 

 variety of forms, habits, and associations, and in the case of the former 

 also present features that do not entirely accord with the descriptions 

 of Cross and Hillebrand. 



Place and Mode of Occurrence 



As the description of these zeolites and of the Table mountains in 

 which they occur are so readily accessible to all, a very brief reference 

 to the surroundings will suffice for our present purpose. At Golden are 

 two socalled table mountains, designated North Table mountain and 

 South Table mountain. Geologically they are but one mountain, con- 

 sisting of soft, nearly horizontal beds of Middle Tertiary age, capped 

 with a thick lava sheet and cut in two by Clear creek. The soft bedded 

 rocks that form the base of the mountain are almost entirely composed 

 of fine andesite ash beds belonging to the Denver Tertiary .f The lava 

 cap consists of two flows of feldspar-basalt that together reach a thick- 

 ness of about 100 feet at the place where the minerals under discussion 

 were obtained. The second flow followed so closely upon the first that 

 no erosion of the first sheet occurred before it was covered by the second 

 sheet. The two flows are of about equal thickness and form a nearly 

 vertical cliff of 100 feet, in the center of which is a horizontal band of 

 very scoriaceous basalt that belongs mainly to the top of the lower flow. 

 This porous band is some 15 feet thick and contains cavities of all sizes 

 up to 6 or 8 feet. The large cavities are drawn out flat in the direction 



* Neues Jahrbuch fur Mineral ogie, etc., vol. i, 1884, p. 250. 



fSee Whitman doss : Geology of die Denver basin, Monograph xxvii, U. S. Geol. Survey, p. 155. 



