4 Sharp Family. 



T3 



is the rich alkivial soil of the river bed, wonderfully prolific of the 

 vegetation belonging to this locality. As we go southward along 

 the valley this treelessness is not so marked, but the entire river 

 bluff is frequently heavily wooded, and it is predicted that the 

 same thing wiil soon be the case in Iowa. Analyses show that 

 the soil is most admirably adapted to sustain vegetation, only 

 requiring the agency of organic matter to perfect its usefulness in 

 this direction. 



One other thing which has been hinted at above, and which is 

 worthy of note, is the general fineness of the material, although 

 the boulder clay is immediately beneath it ; and in many places 

 along the valley I have seen it resting upon sandstone and lime- 

 stane outcropping here and there. 



The material of which the bluffs are composed in Iowa and 

 Missouri and Nebraska is supposed to have been derived from the 

 sandy and chalky beds of the Tertiary and Cretaceous ages of the 

 upper Missouri valley. There are no palaeontological evidences 

 of such derivation, but it is inferred from the similarity of the 

 chemical composition of the bluff soil to that of the beds named. 



If I were to continue this article until I had described every- 

 thing connected with the deposit which possesses any interest to 

 the geologist, the limits assigned to me would have to be indefin- 

 itely extended, and so, observant of the abrupt character of the 

 bluffs themselves, I will bring this paper to an abrupt close. 



W. R. LiGHTON. 



A SHARP FAMILY— THE CACTUSFS. 



THE HATCHET CACTUS. 



One of the most interesting of 

 cactuses is the Pelecyphora, remark- 

 able for its peculiar structure. It is 

 closely related to the mamillarias, of 

 which we shall speak later, having a 

 short cylindrical stem covered with 

 mamillae or tubercles of a flattened 

 form, which has been supposed to 

 bear some resemblance to a hatchet, 

 as the generic name implies. In the 

 place of spines are two rows of flat 

 horny scales, which overlap like the 

 tiles of a roof. The flowers are one 

 to one and a half inches in diameter, 

 and borne near the summit of the 

 plant. There are several series of 

 r; sepals and petals, and numerous sta- 

 mens and stigmas to the flower. 



Pelecyphora aselliformis, figured 



Pelecyphora Asellifoniiis. 



