202 SPARKS FROM A GEOLOGIST'S HAMMER. 



influence of the lakes. Dr. Jared P. Kirtland, of Cleve- 

 land, had published a note on the influence of Lake Erie; 

 but, aside from the phenomena connected with the growth 

 of vegetation, and the presence of southern birds and in- 

 sects, he recorded no exact data beyond a few single obser- 

 vations.* He states that killing autumnal frosts are about 

 a month later on the lake shore than in the interior, and 

 that, in a case of extreme cold, the thermometer marked 

 about six degrees higher at Cleveland than at points some 

 miles back from the lake. Until within a few years ob- 

 servations did not exist from which the influence of the 

 lakes could be deduced in any numerical form. But un- 

 der the Smithsonian system continued for many years, 

 and more lately adopted, to some extent, by the Agri- 

 cultural Bureau, an aggregate of data has resulted which, 

 combined with the observations of the United States Lake 

 Survey, and with meteorological tables in the possession of 

 private parties, has enabled the writer for the first time 

 to eliminate, and express in a series of isothermal curves, 

 the proper influence of the Great Lakes especially Lake 

 Michigan in modifying the climate of each season, of the 

 whole year, and of each month in the year. It is believed 

 the general purport of the tables and charts can be made 

 intelligible to the general reader. f 



* J. P. Kirtland, Amer. Jour, Scl, II, xiii, 215 and 294. 



t Memoirs on this subject by the present writer maybe found as follows: 

 *' The Grand Traverse Region: a report on the Geological and Industrial Re- 

 sources of the Counties of Antrim^ Grand Traverse, Benzie and Leelanaw in the 

 Lower Peninsula of Michigan, 8vo, 82 pp. with Map and an Appendix of 16 pp. 

 on Palaeontology, 1866; The Fruit-bearing Belt of Michigan, Proc. Amer. 

 Association, 1866, pp. 84-89; The Isothermals of the Lake Region, Proc. 

 Amer. Assoc., 1870, pp. 106117; Report on the Progress of the State Geological 

 Survey of Michigan, Lansing, 1871 ; Walling' s Atlas of Michigan, 1873 ; Michigan : 

 being Condensed Popular Sketches of the Topography, Climate and Geology of 

 the State, 8vo, 121 pp. 1873; Zeitschrift der dsterreichischen Gesellschaft fur Me- 

 teorologie, vol. vii, p. 351 and viii, p. 40, February 1, 1873; The Climate of Mich- 



