MARYLAND GEOLOGICAL SUBVET 81 



preservation. They have been but slightly disturbed since deposited 

 and evidently now occupy the same relative positions which they did at 

 the time when they lived. 



The Pliocene.' 

 Within Maryland the Lafayette is the only formation which has been 

 referred to this period. The age of the Lafayette has long been in doubt 

 and there is not yet sufficient data to correlate it definitely with any 

 period. All that can be said is that it is younger than the Miocene which 

 it covers and older than the oldest Pleistocene beds found in the same 

 vicinity. Within this State no fossils have been found of Pliocene 

 age in the deposit. Elsewhere fossil plants and animals alleged to 

 have been discovered within the Lafayette are not of a character suffi- 

 ciently definite to determine its age. It is, however, certain that, after 

 the deposition of the Miocene beds, there was a long interval of erosion 

 before deposition of the Lafayette beds began. Likewise, at the close 

 of Lafayette deposition, another long period of erosion occurred before 

 the Columbia deposits which are of Pleistocene age were laid down. 

 The Lafayette formation thus occupies a stratigraphic position between 

 the youngest known Pliocene and the oldest known Pleistocene in the 

 vicinity, and is separated from each by a long period, during which 

 erosion was in progress. These facts, together with the absence of any 

 undoubted Pliocene deposits in this region, have led to the reference 

 of the Lafayette formation to the latter period. This is, however, only 

 a provisional correlation and more positive evidence is needed before 

 the question can be regarded as settled. 



THE LAFAYETTE FORMATION. 



The Lafaj'ette formation has been named from Lafayette County, 

 Miss., where Hilgard found it typically developed. It consists of clay, 

 loam, 'sand and gravel mixed together in varying proportions. It is 

 developed in a terrace which is stratigraphically older and lies topo- 



* A fuller discussion of the Pliocene In Maryland may be liad by consulting 

 the report on Pliocene and Pleistocene, Md. Geol. Survey, 1906. 



