224 TI1E GEOLOGY OF MINNESOTA. 



[St. Croix sandstone. 



over. The only point at which a useful section of their composition could 

 be had was at Hokah. The general section at this place, as nearly as it 

 could be made out, is as follows, in descending order. 



General section at Hokah. 



Feet. 



St. Lawrence limestone, about 200 



Slope unseen (probably transition, argillaceous beds) 30 



Sandstone, line of constant exposure - . 30 



Slope, rock unseen, (probably crumbling sand) 30 

 Whitman's quarry made up as follows : 



1. Broken, shaly, and sandy, crumbling and fragmentary 10 



2. Shale bed, greenish with remains of trilobitps - 1 



3. Tough, persistent layers, like an ur.clurated, arenaceous shale, with green sand, in 



thin layers 12 



4. Crumbling sand, in oblique stratification. 3 

 Rock very similar to Nos. 3 and 4 extends downward, covering the horizon of an old quarry 



east of llokah, now abandoned as worthless, embracing a thickness that is generally a 

 turfed slope of about 150 



Busty, coarsely arenaceous sandrock with Lingula 10 



Crumbling, white sandrock, massive 25 



Variegated, arenaceous quartzyte, purple, and white, hard and persistent, level with the top 



of the dam, 

 Massive white sandrock 20 



Total rock, about 523 



The hight of Mt. Tom, at Hokah, by aneroid, above the flood-plain, was 

 found to be 530 feet. 



At an old quarry east of Hokah, and across Thompson's creek, now 

 abandoned because the rock is worthless for all purposes, the general aspect 

 of the layers is much like that at Whitman's quarry, but the sand is less 

 firmly cemented, making a stone not so good. It is a shaly and arenaceous 

 sandstone, of coarse and fine grain, marked with fucoids and abundant 

 greensand, and is below the stratigraphical level of Whitman's. In the 

 same bluff, about twenty-five feet higher, is a blind shoulder or terrace 

 which is more likely to contain the layers of Whitman's quarry. This 

 stone, as taken from Whitman's quarry, although very shaly, becomes firm 

 and enduring on exposure. 



At Houston, the bluffs north of the village are 520 feet in hight, and of 

 this the lower 420 feet at least belongs to the St. Croix sandstone. They 

 probably contain the St. Croix twenty feet further up, shown by the toppling 

 over of huge blocks of St. Lawrence limestone, from the crumbling out of 

 friable sandrock along the salient angles of the bluffs. The interval of these 



