I keep hearing you all refer to finding "silver". Are these just nickels/dimes before 1950? I see nickels from the 40's all the time...I found a 1943 dime and a 1938 nickel at work in the register the other day. Are there certain silvers worth more than others? What are the most important/valuable coins you can find in the states? Sorry for so many questions I'm just getting started with detecting.