84 



on the road side, we observed that the lowest stratum exposed is 

 made up of rounded and water-worn stones, consisting chiefly of 

 the blue and gray limestone of the country, but mixed with those 

 of a dark granite or sienite and quartz, which are certainly drift 

 bowlders and from a distance. There is a stratum of sand over 

 the pebbles, but it is quite disturbed, and varies in thickness from 

 two feet to eight inches in different parts of the exposed section. 

 Over this is a layer of fine clayey sand, having more distinctly 

 the appearance of an aqueous deposit, and upon this is the usual 

 soil of the country, consisting of brown loam, somewhat sandy in 

 its character. On traversing the country to the northwest of this 

 gravel bed, we found extensive ledges of naked blue and gray 

 limestone rocks, the surface of which bore strong marks of aque- 

 ous abrasion, and in many places deep holes have been made in 

 the rocks, by the action of water, and perhaps of drift bowlders. 

 Loose rounded rocks of granite, sienite, and quartz, strangers to 

 this region, occur scattered over the surface of the ledges, and 

 are a portion of the northern drift deposit. 



Your committee reserve their opinion as to the cause of these 

 phenomena until they can gain more light on this very interesting 

 subject, and hope to have occasion to report further progress 

 some time during the summer, when they shall have made more 

 extended researches, and visited other localities, where frozen 

 wells are stated to exist. 



For the committee, 



Charles T. Jackson. 



John H. Blake. 



Prof. W. B. Rogers described in this connection the so-called 

 natural icehouses in Virginia ; in these cases the ice penetrates 

 the large interstices of the rocks during winter, and the natural 

 covering of the soil, a poor conductor of heat, protects from the 

 heat of the sun in summer. He observed that it was important 

 to consider the mean temperature of the place in explaining the 

 phenomena of frozen wells ; the mean annual temperature of 

 Brandon is only 45° F. ; of the winter 20°, of the spring 40° ; 

 giving for the winter and spring a temperature of 30°, or 2° less 

 than the freezing point of water — in fact, at about the depth of 30 

 or 40 feet, a reversal of the seasons takes place, so slow is the 



