Your question cannot be answered without competent geneaology. Competent geneaology requires that you document every element of your family tree. The way to identify ancestors is by documenting the family relationships generation by generation, town by town. The same or similar family name does not mean the individuals in questions were part of the family you are researching. Likewise, differences in spelling are irrelevant--consistency in spelling is a modern invention, things were spelled as they sounded to the recorder, and standards of literacy varied greatly. You cannot assume without documentation, even if the name appears the same.

The first step is to interview the oldest living members of your family in order to determine where your Clark or Clarke family has lived in the U.S., and if you can locate any family documents from Scotland, you are ahead of the game. If you can find their immigration records, it will frequently tell you the town in Scotland they came from. These records are called Declarations of Naturalization, Intentions. If there is any family knowledge as to the town or district the family lived in in Scotland, that is very important. Knowing the spouses' names and tracing the spouses' family can be very helpful when a man you are researching has a very common name--in many Scottish records the wife's maiden name was recorded along with her husband's, making it possible to find him even if his name is John Smith [or James Clarke].

The key is to find where the family has been located over the years, and then search census [both Federal & State],church, property, tax and probate [wills, etc.] records in each place where your family has been located. A good place to get started is www.familysearch.org. Once you have information about your Clarkes, you may wish to search the Old Parish Registers in Scotland, which you can do online for a fee at www.scotlandspeople.gov.uk. You can also search the UK/Scottish Census' online. You may wish to contact an Historical Society in any community you identify in Scotland where your Clarkes have lived, as they can provide assistance and sometimes record look ups for a modest fee.

I hope you will take the time to investigate your family history. It may sound complicated, and like a lot of work, but it is a great deal of fun. Good luck!