HOUSTON COUNTY. 217 



Geological structure.] 



of the former. Both sorts are rough on the edges and on the prominent ribs beneath, and are 

 barely pointed. The carrion-flower, Smilax herbacea, L. was identified in the ravines on the north 

 side of the valley at Houston.] 



It is noticeable that many of the valleys, particularly those running east and west, as Crooked 

 creek valley, have the bluffs along the north side of the creek destitute, or nearly so, of timber, 

 but are heavily timbered along the opposite bluffs, on the south side. This may be due to warm 

 days in winter or early spring when the sap may have started in the trees on the north bluffs, fol- 

 lowed by severely cold weather, before the actual setting in of steady warm weather. Of course 

 the sun's heat would be quickest felt on the bluffs facing south. This process repeated for a good 

 many years, would injure and at last destroy the timber on the north bluffs, if it were ever possible 

 for trees to have come to maturity there, while timber on the south bluffs would escape these sud- 

 den changes, owing to the shaded condition of the bluffs during the warmest portion of the day, 

 and would only experience a steady increase of warmth due f o the progress of the season.* 



At La Crescent Mr. J. S. Harris has an apple-tree that has been grow- 

 ing twenty-six years. It was planted in 1857, and is probably the oldest 

 of its kind in the state. Its diameter is seventeen inches at eighteen inches 

 from the ground. It spreads thirty-six feet and has a hight of eighteen feet. 

 Its fruit is known as the St. Lawrence apple. 



* 



THE GEOLOGICAL STRUCTURE OF HOUSTON COUNTY. 







The rocks of Houston county are embraced wholly within the Lower 

 Silurian and Cambrian ages. They are as follows : 



The Hudson River shales and Trenton limestone, confined to the south- 

 western quarter, being of the Lower Silurian. 



The Cambrian, made up of a succession of alternating friable sandstones 

 and magnesian limestones, as follows, in descending order : 



(1) St. Peter sandstone, in an irregular area surrounding the area of the 

 Trenton above. 



(2) The Shakopee limestone, in the upper river valleys. 



(3) The Jordan sandstone, in the upper portion of the river valleys. 



(4) The St. Lawrence limestone, in the bluifs of the rivers. 



(5) The St. Croix sandstone, in the river bluffs. 



The accompanying map of the county, plate 8, shows the superficial 

 areas to which the most important of these formations pertain. The Jor- 

 dan, Shakopee and St. Lawrence are represented by a single color, as they are 

 closely associated in the production of important topographical characters. 

 Owing to the frequent deep valleys the geographical boundaries of the 

 formations make very crooked and tortuous lines. Although these valleys 



*Carrer noted this peculiarity in the distribution of timber (second edit-on of Carver's Travels^ p. 34). He says: " In 

 many places pyramids of rocks appeared, resembling old ruinous towers; at others amazing precipices, and what is more 

 remarkable, whilst this scene presented itself on one side, the opposite side oi the same mountain was crowded with the 

 finest herbage, which gradually ascended to its summit." 



