294 GEOLOGY OF THE DENVER BASIX. 



The general sequence of formation of the minerals is as follows: (1) 

 Wine-yellow calcite, (2) stilbite and laumontite, (3) thomsonite in reddish 

 spherules, (4) stilbite, (5) chabazite, (6) thomsonite, (7) analcite, (8) 

 apophyllite, (9) mesolite. The first three of this series occur in the reddish 

 deposits, described below; the others in the white or colorless series. No 

 definite places can be assigned to levynite, scolecite, or natrolite. 



Reddish deposits of the first period. — The colored minerals of the first period of 

 zeolitic formation deserve some special description. They are found in the 

 irregular cavities of the more or less broken, scoriaceous crust of the lower 

 basalt sheet; in fissures leading down into the amygdaloidal zone, and in 

 certain of the vesicles of this zone. They also appear to a less extent in 

 some cracks and cavities of the earliest streams 100 feet below the main 

 sheet. The character of this earlier zeolitic formation will he most clearly 

 understood if the deposits of the vesicles are first described. 



At almost any point of the circumference of North Table Mountain, 

 within the zeolitic /one, it maybe noticed that some of the cavities contain 

 reddish-yellow deposits. The number of cavities containing such masses 

 is relatively small, and while some of them may exhibit deposits a foot or 

 more in thickness, directly adjoining pores are entirely free from anything 

 resemblimg the formation in question. On examination of the deposit in 

 some large cavity it is usually found to he characterized as follows: 



In the first place, the mass is always found directly in contact with 

 the basalt, no intervening mineral of earlier formation having been seen 

 in any case. This deposit is therefore the first of the secondary mineral 

 secretions. 



Secondly, it is a striking characteristic that all these reddish zeolitic 

 masses are horizontally bedded, and that when a cavity is hut partially 

 filled it is invariably the lower part which contains the mass, so that there 

 remains a smooth, level Moor to such a vesicle. In no case does the deposit 

 of this period form concentric shells in the manner usual where there is a 

 succession of zeolites in the pores of a volcanic rock. 



Lastly, there is a sequence of species corresponding to the growth 

 from below upward. Each stratum is quite uniform in composition, while 

 successive ones niav change materially. 



