1884,] NATURAL SCIENCES OP PHILADELPHIA. 69 



probably caused by the colon}'^ pushing up the earth from two 

 independent centres, which in the course of time united. Future 

 labors might possibly correct this, and round the outlines to their 

 normal shape. I saw one formicary in South Park, which was 

 established under a large stone, along the edges of which the 

 gates or openings were placed. Another was seen on the Divide 

 beyond Colorado Springs, domiciled under an old log in a grove. 

 Here several ant-lions (Myrmeleon) had established themselves, 

 cannily digging their pits near the very gates of the formicary, 

 quite in the route of the outcoming and ingoing emmets. The 

 largest mound seen by me, and larger than any reported to me, 

 was found near the summit of the Ute Pass. It was a conical 

 heap, four feet long and about one foot high, and looked like a 

 small haycock. 



Thatching the Hoofs. — 

 This Ute Pass ant-hill was 

 thickly covered or thatched 

 with bits of wood, fallen 

 needles and broken sprigs of 

 pine, which had been gath- '"'-'-SSS^iil^lv.^^^^ 



ered from the forest debris, "'" -'-^^■'^^:^■"'^'^'-'^^■■'' 



1 • \ J J.1 • j.\ • FiQ.2. Mound with Square Base. —Dakota. 



lying abundantly in the vi- ^ 



cinit3\ All other mounds in South Park and around Leadville 

 were covered in a like manner, with stalks of grass, twigs, and 

 similar rubbish. 



The Dakota ant-hills are thatched in precisely the same way, 

 so that one can easily see the propriet}^ of giving the little artisan 

 the popular title of the Thatching ant. As the colony increases its 

 numbers, and the necessity of internal domestic economy requires 

 enlargement of the nurseries, rooms and galleries, the excavated 

 soil is brought up and naturally is laid upon the thatching. In 

 course of time a new roof of chips and clipped grass is overlaid, 

 and thus in the ordinary growth of a mound there would be an 

 alternation of layers of earth and vegetable substance, the latter 

 falling into decay in due season. This theory of the growth of 

 a hill is confirmed by samples of material taken by Dr. De Puy 

 from the interior of the Dakota mounds, which consists of partly 

 decomposed straw, mixed in smaller proportion with soil. The 

 mound-making ants of the Alleghenies {Formica exsectdides) 



