98 PHYSICAL GEOGEAPHY. 



in a good state of preservation. This wood had its origin to 

 the northward of where it is now found without doubt, but 

 exactly where and how far, we can probably never know. 



Fossils. No fossils of any kind have been found in the drift 

 of Iowa which may be said to properly belong to it. Those 

 found in it belong to other formations, and have been trans- 

 ported from their original strata together with the other 

 materials of the drift. Mr. P. Mclsaac, of Waterloo, Iowa, 

 has shown me a specimen of a Cretaceous Ammonite which he 

 found in the drift near that place, and a fragment of a Baculite 

 has been found in the drift near Iowa City. Coal-measure 

 fossils have been found in boulders in Des Moines county, and 

 Lower Silurian fossils have been previously mentioned as occur- 

 ring in the limestone drift-boulders of central Iowa. Some 

 shark's teeth have been found in the drift of southeastern 

 Iowa, and supposed by others to have originated in a northern 

 prolongation of the Gulf-border Tertiary formations ; but it 

 seems not improbable that they originated in the Cretaceous 

 strata to the northwestward, and were transported thither dur- 

 ing the Glacial epoch; although, it is not to be denied that they 

 approach more nearly to Tertiary than to Cretaceous forms . The 

 last indication of glacial action we shall notice here, is that of 



Moraines (V) The phenomena here referred to with doubt as 

 moraines, may be properly regarded as of doubtful character; 

 but yet, they are nevertheless well worthy of notice. They 

 seem at least to be accumulations of drift material which 

 mark periodical arrests of the recedence by melting, of the 

 glaciers to the northward as the Glacial epoch was drawing to 

 a close, as a consequence of a gradual change of climate. 

 They consist of two well-marked but slight elevations in the 

 general surface of the country. They both have an easterly 

 and westerly direction, and are gradually lost at either end 

 in the general prairie surface. One of them extends through 

 the northern part of Boone and Story counties, and is known 

 to the inhabitants as " Mineral ridge." It consists to a con- 

 siderable extent of a collection of slightly raised ridges and 

 knolls, sometimes interspersed with small, shallow ponds; 



