No permanent abodes were erected by the miners in this region, no mounds were constructed, but the indications all point to a summer’s residence only and a return to the south with the accumulation of their toil when the severities of winter approached. Frederick von Hellwald expresses it as his opinion that the Mexicans obtained all their copper from the Lake Superior mines, and adds that no evidences exist that copper was mined in Mexico or Central America prior to the Spanish Conquest.[77] Humboldt affirms that various metals were mined by the Mexicans, but does not specify copper.[78] Col. Whittlesey and Prof. Andrews estimate that in the ancient Lake Superior mines worked by the Mound-builders, the removed metal would aggregate a length of one hundred and fifty miles in veins of varying thickness. This fact certainly indicates that great supplies were transported southward. This remarkable people was evidently possessed of the beginnings of science; at least if the Davenport and Cincinnati tablets are genuine, astronomy must have received considerable attention at their hands. In the former tablet we observe a cycle divided into twelve months (which, however, is so modern and coincides so strictly with our division as to excite suspicion of fraud), while in the latter we have the number 368 as the sum of the products of the longer and shorter lines, suggestive of an approximation to the number of days in a year. Other supposed astronomical instruments have been discovered in the mounds of Ohio, and several of these, _antique tubes, telescope devices_, were discovered in the course of excavations made in 1842 in the most easterly of the Elizabethtown group, West Virginia. Mr. Schoolcraft makes the following statement concerning them: “Several tubes of stone were disclosed, the precise object of which has been the subject of various opinions. The longest measured twelve inches, the shortest eight. Three of them were carved out of steatite, being skillfully cut and polished. The diameter of the tube externally was one inch and four-tenths; the bore eight-tenths of an inch. By placing the eye at the diminished end, the extraneous light is shut from the pupil, and distant objects are more clearly discerned.”[79] A silver figure found in Peru represents a man in the act of studying the heavens through one of these tubes, and Captain Dupaix saw a stone in Mexico bearing the figure of a man sculptured on its side in the act of using a similar tube.[80] [Illustration: Clay Vessels from Mounds in the Mississippi Valley. ¼ Size. (Nat. Mus.)] [Illustration: Clay Tube from an Ohio Mound. ½ Natural Size. (Peabody Mus.)]