text: Bedrock is the native consolidated rock underlying the Earth's surface. Above the bedrock is usually an area of broken and weathered unconsolidated rock in the basal subsoil. The term implies that the rock lies in beds, or strata. Under any given location on the surface of the planet, rock will be found. The term bedrock may be somewhat misleading, since in many locations, the bedrock may change over a short distance, or the technical bedrock may be a thin stratum overlying quite different rock.\nGravel is rock that is of a certain grain size range. In geology, gravel is any loose rock that is at least two millimeters in its largest dimension (about 1/12 of an inch), and no more than 75 millimeters (about 3 inches).\nLoose rock is larger rock piled up loosely and it can move when disturbed by any type of vibration. The type of rock in land slides.\nI have never heard of a drumline\nAn ice age is a period of long-term downturn in the temperature of Earth's climate, resulting in an expansion of the continental ice sheets, polar ice sheets and mountain glaciers ("glaciation"). Glaciologically, ice age is often used to mean a period of ice sheets in the northern and southern hemispheres; by this definition we are still in an ice age (because the Greenland and Antarctic ice sheets still exist). More colloquially, when speaking of the last few million years, ice age is used to refer to colder periods with extensive ice sheets over the North American and Eurasian continents: in this sense, the last ice age ended about 10,000 years ago. This article will use the term ice age in the former, glaciological, sense; and use the term glacial periods for colder periods during ice ages and interglacial for the warmer periods.\nMany glacial periods have occurred during the last few million years, initially at 40,000-year frequency but more recently at 100,000-year frequencies. These are the best studied. There have been four major ice ages in the further past.\nhttp://en.wikipedia.org/wiki/Ice_age\n\ngo to the link below for a documentary\nhttp://a614.g.akamai.net/7/614/2201/v001/aetn.download.akamai.com/2201/thc/classroom/guides/ice_age_study_guide.pdf